diff --git a/CHANGELOG.md b/CHANGELOG.md
index b4baaa2..09165f2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,17 @@
 # Changelog
 
+## [v1.0.0-beta.3](https://github.com/contentstack/contentstack-management-dotnet/tree/v1.0.0-beta.3)
+ - **ContentType & QueryService STJ Migration**
+   - **✅ ContentType Module**: Fully migrated ContentType model and dependencies to System.Text.Json
+   - **✅ QueryService Migration**: Re-enabled and migrated QueryService for content type listing
+   - **✅ Field System**: Converted core Field models (FieldMetadata, Field, FieldRules) to STJ
+   - **✅ ContentModelling**: Updated ContentModelling and Option classes with STJ attributes
+   - **✅ Service Layer**: Migrated CreateUpdateService, FetchDeleteService, and DeleteService
+   - **✅ Web App Integration**: Complete ContentType CRUD interface with modern UI
+   - **✅ Schema Validation**: Added default "Title" field to prevent 422 API errors
+   - **✅ Error Handling**: Enhanced error reporting with detailed API validation messages
+   - **✅ Navigation**: Integrated ContentType management into Stack workflow
+
 ## [v1.0.0-beta.2](https://github.com/contentstack/contentstack-management-dotnet/tree/v1.0.0-beta.2)
  - **System.Text.Json Migration Complete (Beta)**
    - **✅ Core Modules STJ-Only**: Client, User, Organization, and Stack modules fully migrated
diff --git a/Contentstack.Management.Core/ContentstackClient.cs b/Contentstack.Management.Core/ContentstackClient.cs
index 3c5f94c..0cbf678 100644
--- a/Contentstack.Management.Core/ContentstackClient.cs
+++ b/Contentstack.Management.Core/ContentstackClient.cs
@@ -200,7 +200,7 @@ protected void Initialize(HttpClient? httpClient = null)
             SerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull;
             SerializerOptions.PropertyNameCaseInsensitive = true;
 
-            // SerializerOptions.Converters.Add(new FieldJsonConverter()); // Excluded for now
+            SerializerOptions.Converters.Add(new FieldJsonConverter()); // Re-enabled for ContentType support
             SerializerOptions.Converters.Add(new NodeJsonConverter());
             SerializerOptions.Converters.Add(new TextNodeJsonConverter());
         }
diff --git a/Contentstack.Management.Core/Models/BaseModel.cs b/Contentstack.Management.Core/Models/BaseModel.cs
index b8b996c..7be25d7 100644
--- a/Contentstack.Management.Core/Models/BaseModel.cs
+++ b/Contentstack.Management.Core/Models/BaseModel.cs
@@ -15,7 +15,7 @@ public class BaseModel<T>
         public string Uid { get; set; }
 
 
-        public BaseModel(Stack stack, string fieldName, string uid = null)
+        public BaseModel(Stack stack, string fieldName, string? uid = null)
         {
             stack.ThrowIfAPIKeyEmpty();
             if (fieldName == null)
@@ -27,75 +27,75 @@ public BaseModel(Stack stack, string fieldName, string uid = null)
             Uid = uid;
         }
 
-        public virtual ContentstackResponse Create(T model, ParameterCollection collection = null)
+        public virtual ContentstackResponse Create(T model, ParameterCollection? collection = null)
         {
             ThrowIfUidNotEmpty();
 
-            var service = new CreateUpdateService<T>(stack.client.serializer, stack, resourcePath, model, this.fieldName, collection: collection);
+            var service = new CreateUpdateService<T>(stack, resourcePath, model, this.fieldName, collection: collection, stjOptions: stack.client.SerializerOptions);
             return stack.client.InvokeSync(service);
         }
 
-        public virtual Task<ContentstackResponse> CreateAsync(T model, ParameterCollection collection = null)
+        public virtual Task<ContentstackResponse> CreateAsync(T model, ParameterCollection? collection = null)
         {
             ThrowIfUidNotEmpty();
             stack.ThrowIfNotLoggedIn();
 
-            var service = new CreateUpdateService<T>(stack.client.serializer, stack, resourcePath, model, this.fieldName, collection: collection);
+            var service = new CreateUpdateService<T>(stack, resourcePath, model, this.fieldName, collection: collection, stjOptions: stack.client.SerializerOptions);
 
             return stack.client.InvokeAsync<CreateUpdateService<T>, ContentstackResponse>(service);
         }
 
-        public virtual ContentstackResponse Update(T model, ParameterCollection collection = null)
+        public virtual ContentstackResponse Update(T model, ParameterCollection? collection = null)
         {
             ThrowIfUidEmpty();
 
-            var service = new CreateUpdateService<T>(stack.client.serializer, stack, resourcePath, model, this.fieldName, "PUT", collection: collection);
+            var service = new CreateUpdateService<T>(stack, resourcePath, model, this.fieldName, "PUT", collection: collection, stjOptions: stack.client.SerializerOptions);
             return stack.client.InvokeSync(service);
         }
 
-        public virtual Task<ContentstackResponse> UpdateAsync(T model, ParameterCollection collection = null)
+        public virtual Task<ContentstackResponse> UpdateAsync(T model, ParameterCollection? collection = null)
         {
             stack.ThrowIfNotLoggedIn();
             ThrowIfUidEmpty();
 
-            var service = new CreateUpdateService<T>(stack.client.serializer, stack, resourcePath, model, this.fieldName, "PUT", collection: collection);
+            var service = new CreateUpdateService<T>(stack, resourcePath, model, this.fieldName, "PUT", collection: collection, stjOptions: stack.client.SerializerOptions);
 
             return stack.client.InvokeAsync<CreateUpdateService<T>, ContentstackResponse>(service);
         }
 
-        public virtual ContentstackResponse Fetch(ParameterCollection collection = null)
+        public virtual ContentstackResponse Fetch(ParameterCollection? collection = null)
         {
             stack.ThrowIfNotLoggedIn();
             ThrowIfUidEmpty();
 
-            var service = new FetchDeleteService(stack.client.serializer, stack, resourcePath, collection: collection);
+            var service = new FetchDeleteService(stack, resourcePath, collection: collection, stjOptions: stack.client.SerializerOptions);
             return stack.client.InvokeSync(service);
         }
 
-        public virtual Task<ContentstackResponse> FetchAsync(ParameterCollection collection = null)
+        public virtual Task<ContentstackResponse> FetchAsync(ParameterCollection? collection = null)
         {
             stack.ThrowIfNotLoggedIn();
             ThrowIfUidEmpty();
 
-            var service = new FetchDeleteService(stack.client.serializer, stack, resourcePath, collection: collection);
+            var service = new FetchDeleteService(stack, resourcePath, collection: collection, stjOptions: stack.client.SerializerOptions);
             return stack.client.InvokeAsync<FetchDeleteService, ContentstackResponse>(service);
         }
 
-        public virtual ContentstackResponse Delete(ParameterCollection collection = null)
+        public virtual ContentstackResponse Delete(ParameterCollection? collection = null)
         {
             stack.ThrowIfNotLoggedIn();
             ThrowIfUidEmpty();
 
-            var service = new FetchDeleteService(stack.client.serializer, stack, resourcePath, "DELETE", collection: collection);
+            var service = new FetchDeleteService(stack, resourcePath, "DELETE", collection: collection, stjOptions: stack.client.SerializerOptions);
             return stack.client.InvokeSync(service);
         }
 
-        public virtual Task<ContentstackResponse> DeleteAsync(ParameterCollection collection = null)
+        public virtual Task<ContentstackResponse> DeleteAsync(ParameterCollection? collection = null)
         {
             stack.ThrowIfNotLoggedIn();
             ThrowIfUidEmpty();
 
-            var service = new FetchDeleteService(stack.client.serializer, stack, resourcePath, "DELETE", collection: collection);
+            var service = new FetchDeleteService(stack, resourcePath, "DELETE", collection: collection, stjOptions: stack.client.SerializerOptions);
 
             return stack.client.InvokeAsync<FetchDeleteService, ContentstackResponse>(service);
         }
diff --git a/Contentstack.Management.Core/Models/ContentModelling.cs b/Contentstack.Management.Core/Models/ContentModelling.cs
index a43eac7..21f58a3 100644
--- a/Contentstack.Management.Core/Models/ContentModelling.cs
+++ b/Contentstack.Management.Core/Models/ContentModelling.cs
@@ -1,55 +1,53 @@
 using System.Collections.Generic;
 using System.Linq;
+using System.Text.Json.Serialization;
 using Contentstack.Management.Core.Models.Fields;
-using Newtonsoft.Json;
 
 namespace Contentstack.Management.Core.Models
 {
-    [JsonObject(ItemNullValueHandling = NullValueHandling.Ignore)]
     public class ContentModelling
     {
-        [JsonProperty(propertyName: "title")]
-        public string Title { get; set; }
+        [JsonPropertyName("title")]
+        public string? Title { get; set; }
 
-        [JsonProperty(propertyName: "uid")]
-        public string Uid { get; set; }
+        [JsonPropertyName("uid")]
+        public string? Uid { get; set; }
 
-        [JsonProperty(propertyName: "description")]
-        public string Description { get; set; }
+        [JsonPropertyName("description")]
+        public string? Description { get; set; }
 
-        [JsonProperty(propertyName: "field_rules")]
-        public List<FieldRules> FieldRules { get; set; }
+        [JsonPropertyName("field_rules")]
+        public List<FieldRules>? FieldRules { get; set; }
 
-        [JsonProperty(propertyName: "schema")]
-        public List<Field> Schema { get; set; }
+        [JsonPropertyName("schema")]
+        public List<Field>? Schema { get; set; }
 
-        [JsonProperty(propertyName: "global_field_refs")]
-        public List<GlobalFieldRefs> GlobalFieldRefs { get; set; }
+        [JsonPropertyName("global_field_refs")]
+        public List<GlobalFieldRefs>? GlobalFieldRefs { get; set; }
 
-        [JsonProperty(propertyName: "options")]
-        public Option Options { get; set; }
+        [JsonPropertyName("options")]
+        public Option? Options { get; set; }
     }
 
-    [JsonObject(ItemNullValueHandling = NullValueHandling.Ignore)]
     public class Option
     {
-        [JsonProperty(propertyName: "title")]
-        public string Title { get; set; }
+        [JsonPropertyName("title")]
+        public string? Title { get; set; }
 
-        [JsonProperty(propertyName: "sub_title")]
-        public List<string> SubTitle { get; set; }
+        [JsonPropertyName("sub_title")]
+        public List<string>? SubTitle { get; set; }
 
-        [JsonProperty(propertyName: "singleton")]
+        [JsonPropertyName("singleton")]
         public bool Singleton { get; set; }
 
-        [JsonProperty(propertyName: "is_page")]
+        [JsonPropertyName("is_page")]
         public bool IsPage { get; set; }
 
-        [JsonProperty(propertyName: "url_pattern")]
-        public string UrlPattern { get; set; }
+        [JsonPropertyName("url_pattern")]
+        public string? UrlPattern { get; set; }
 
-        [JsonProperty(propertyName: "url_prefix")]
-        public string UrlPrefix { get; set; }
+        [JsonPropertyName("url_prefix")]
+        public string? UrlPrefix { get; set; }
 
     }    
 }
diff --git a/Contentstack.Management.Core/Models/ContentType.cs b/Contentstack.Management.Core/Models/ContentType.cs
index 793fc16..8bd6c50 100644
--- a/Contentstack.Management.Core/Models/ContentType.cs
+++ b/Contentstack.Management.Core/Models/ContentType.cs
@@ -39,7 +39,7 @@ public Query Query()
         /// </example>
         /// <param name="model">IContentType for updating Content Type.</param>
         /// <returns></returns>
-        public override ContentstackResponse Create(ContentModelling model, ParameterCollection collection = null)
+        public override ContentstackResponse Create(ContentModelling model, ParameterCollection? collection = null)
         {
             return base.Create(model, collection);
         }
@@ -56,7 +56,7 @@ public override ContentstackResponse Create(ContentModelling model, ParameterCol
         /// </example>
         /// <param name="model">IContentType for updating Content Type.</param>
         /// <returns></returns>
-        public override Task<ContentstackResponse> CreateAsync(ContentModelling model, ParameterCollection collection = null)
+        public override Task<ContentstackResponse> CreateAsync(ContentModelling model, ParameterCollection? collection = null)
         {
             return base.CreateAsync(model, collection);
         }
@@ -73,7 +73,7 @@ public override Task<ContentstackResponse> CreateAsync(ContentModelling model, P
         /// </example>
         /// <param name="model">IContentType for updating Content Type.</param>
         /// <returns></returns>
-        public override ContentstackResponse Update(ContentModelling model, ParameterCollection collection = null)
+        public override ContentstackResponse Update(ContentModelling model, ParameterCollection? collection = null)
         {
             return base.Update(model, collection);
         }
@@ -90,7 +90,7 @@ public override ContentstackResponse Update(ContentModelling model, ParameterCol
         /// </example>
         /// <param name="model">IContentType for updating Content Type.</param>
         /// <returns></returns>
-        public override Task<ContentstackResponse> UpdateAsync(ContentModelling model, ParameterCollection collection = null)
+        public override Task<ContentstackResponse> UpdateAsync(ContentModelling model, ParameterCollection? collection = null)
         {
             return base.UpdateAsync(model, collection);
         }
@@ -105,7 +105,7 @@ public override Task<ContentstackResponse> UpdateAsync(ContentModelling model, P
         /// </code></pre>
         /// </example>
         /// <returns>The <see cref="ContentstackResponse"/>.</returns>
-        public override ContentstackResponse Fetch(ParameterCollection collection = null)
+        public override ContentstackResponse Fetch(ParameterCollection? collection = null)
         {
             return base.Fetch(collection);
         }
@@ -120,7 +120,7 @@ public override ContentstackResponse Fetch(ParameterCollection collection = null
         /// </code></pre>
         /// </example>
         /// <returns>The Task.</returns>
-        public override Task<ContentstackResponse> FetchAsync(ParameterCollection collection = null)
+        public override Task<ContentstackResponse> FetchAsync(ParameterCollection? collection = null)
         {
             return base.FetchAsync(collection);
         }
@@ -135,7 +135,7 @@ public override Task<ContentstackResponse> FetchAsync(ParameterCollection collec
         /// </code></pre>
         /// </example>
         /// <returns>The <see cref="ContentstackResponse"/>.</returns>
-        public override ContentstackResponse Delete(ParameterCollection collection = null)
+        public override ContentstackResponse Delete(ParameterCollection? collection = null)
         {
             return base.Delete(collection);
         }
@@ -150,11 +150,12 @@ public override ContentstackResponse Delete(ParameterCollection collection = nul
         /// </code></pre>
         /// </example>
         /// <returns>The Task.</returns>
-        public override Task<ContentstackResponse> DeleteAsync(ParameterCollection collection = null)
+        public override Task<ContentstackResponse> DeleteAsync(ParameterCollection? collection = null)
         {
             return base.DeleteAsync(collection);
         }
 
+        /*
         /// <summary>
         /// <see cref="Models.Entry" /> is the actual piece of content created using one of the defined content types.
         /// </summary>
@@ -176,5 +177,6 @@ public Entry Entry(string uid = null)
             ThrowIfUidEmpty();
             return new Entry(stack, Uid, uid);
         }
+        */
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/DateField.cs b/Contentstack.Management.Core/Models/Fields/DateField.cs
index 84f3d4e..1712ed1 100644
--- a/Contentstack.Management.Core/Models/Fields/DateField.cs
+++ b/Contentstack.Management.Core/Models/Fields/DateField.cs
@@ -1,13 +1,13 @@
 using System;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
     public class DateField : Field
     {
-        [JsonProperty(propertyName: "startDate")]
+        [JsonPropertyName("startDate")]
         public string StartDate { get; set; }
-        [JsonProperty(propertyName: "endDate")]
+        [JsonPropertyName("endDate")]
         public string EndDate { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/ExtensionField.cs b/Contentstack.Management.Core/Models/Fields/ExtensionField.cs
index 1c2b144..abc4996 100644
--- a/Contentstack.Management.Core/Models/Fields/ExtensionField.cs
+++ b/Contentstack.Management.Core/Models/Fields/ExtensionField.cs
@@ -1,14 +1,15 @@
 using System;
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
     public class ExtensionField : Field
     {
-        [JsonProperty(propertyName: "extension_uid")]
+        [JsonPropertyName("extension_uid")]
         public string extension_uid { get; set; }
-        [JsonProperty(propertyName: "config")]
-        public Dictionary<string, object> config { get; set; }
+        [JsonPropertyName("config")]
+        public Dictionary<string, JsonElement> config { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/Field.cs b/Contentstack.Management.Core/Models/Fields/Field.cs
index cc86ebd..25676d6 100644
--- a/Contentstack.Management.Core/Models/Fields/Field.cs
+++ b/Contentstack.Management.Core/Models/Fields/Field.cs
@@ -1,45 +1,44 @@
 using System;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
-    [JsonObject(ItemNullValueHandling = NullValueHandling.Ignore)]
     public class Field
     {
         /// <summary>
         /// Determines the display name of a field. It is a mandatory field.
         /// </summary>
-        [JsonProperty(propertyName: "display_name")]
-        public string DisplayName { get; set; }
+        [JsonPropertyName("display_name")]
+        public string? DisplayName { get; set; }
         /// <summary>
         /// Represents the unique ID of each field. It is a mandatory field.	
         /// </summary>
-        [JsonProperty(propertyName: "uid")]
-        public string Uid { get; set; }
+        [JsonPropertyName("uid")]
+        public string? Uid { get; set; }
         /// <summary>
         /// Determines what value can be provided to the Title field.	
         /// </summary>
-        [JsonProperty(propertyName: "data_type")]
-        public string DataType { get; set; }
+        [JsonPropertyName("data_type")]
+        public string? DataType { get; set; }
         /// <summary>
         /// Allows you to enter additional data about a field. Also, you can add additional values under 'field_metadata'.
         /// </summary>
-        [JsonProperty(propertyName: "field_metadata")]
-        public FieldMetadata FieldMetadata { get; set; }
+        [JsonPropertyName("field_metadata")]
+        public FieldMetadata? FieldMetadata { get; set; }
 
-        [JsonProperty(propertyName: "multiple")]
+        [JsonPropertyName("multiple")]
         public bool Multiple { get; set; }
 
-        [JsonProperty(propertyName: "mandatory")]
+        [JsonPropertyName("mandatory")]
         public bool Mandatory { get; set; }
 
-        [JsonProperty(propertyName: "unique")]
+        [JsonPropertyName("unique")]
         public bool Unique { get; set; }
 
         /// <summary>
         /// Presentation widget for text fields (e.g. dropdown, checkbox).
         /// </summary>
-        [JsonProperty(propertyName: "display_type")]
-        public string DisplayType { get; set; }
+        [JsonPropertyName("display_type")]
+        public string? DisplayType { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/FieldMetadata.cs b/Contentstack.Management.Core/Models/Fields/FieldMetadata.cs
index b384edf..ab269ff 100644
--- a/Contentstack.Management.Core/Models/Fields/FieldMetadata.cs
+++ b/Contentstack.Management.Core/Models/Fields/FieldMetadata.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
@@ -8,89 +9,90 @@ public class FieldMetadata
     {
         /// <summary>
         /// Allows you to set default fields for content types.
+        /// API can send both boolean and string values, so using JsonElement for flexibility.
         /// </summary>
-        [JsonProperty(propertyName: "_default")]
-        public string Default { get; set; }
+        [JsonPropertyName("_default")]
+        public JsonElement? Default { get; set; }
 
         /// <summary>
         /// Allows you to set a default value for a field.
         /// </summary>
-        [JsonProperty(propertyName: "default_value")]
-        public object DefaultValue { get; set; }
+        [JsonPropertyName("default_value")]
+        public object? DefaultValue { get; set; }
 
         /// <summary>
         /// Determines whether the editor will support rich text, and is set to ‘true’ by default for Rich Text Editors.
         /// </summary>
-        [JsonProperty(propertyName: "allow_rich_text")]
+        [JsonPropertyName("allow_rich_text")]
         public bool AllowRichText { get; set; }
 
         /// <summary>
         /// Allows you to provide the content for the Rich text editor field.
         /// </summary>
-        [JsonProperty(propertyName: "description")]
-        public string Description { get; set; }
+        [JsonPropertyName("description")]
+        public string? Description { get; set; }
 
         /// <summary>
         /// Provides multi-line capabilities to the Rich text editor.
         /// </summary>
-        [JsonProperty(propertyName: "multiline")]
+        [JsonPropertyName("multiline")]
         public bool Multiline { get; set; }
 
         /// <summary>
         /// Lets you enable either the basic, custom, or advanced editor to enter your content.
         /// </summary>
-        [JsonProperty(propertyName: "rich_text_type")]
-        public string RichTextType { get; set; }
+        [JsonPropertyName("rich_text_type")]
+        public string? RichTextType { get; set; }
 
         /// <summary>
         /// If you choose the Custom editor, then the options key lets you specify the formatting options you prefer for your RTE toolbar,
         /// e.g., "options": ["h3", "blockquote", "sup"]
         /// </summary>
-        [JsonProperty(propertyName: "options")]
-        public List<string> Options { get; set; }
+        [JsonPropertyName("options")]
+        public List<string>? Options { get; set; }
 
         /// <summary>
         /// This key determines whether you are using the older version of the Rich Text Editor or the latest version.
         /// The value of 1 denotes that it is an older version of the editor, while 3 denotes that it is the latest version of the editor.
         /// </summary>
-        [JsonProperty(propertyName: "version")]
+        [JsonPropertyName("version")]
         public int Version { get; set; }
 
         /// <summary>
         /// Lets you assign a field to be a markdown by setting its value to ‘true’.
         /// </summary>
-        [JsonProperty(propertyName: "markdown")]
+        [JsonPropertyName("markdown")]
         public bool Markdown { get; set; }
 
         /// <summary>
         /// Allows you to provide a hint text about the values that need to be entered in an input field, e.g., Single Line Textbox.
         /// This text can be seen inside the field until you enter a value.
         /// </summary>
-        [JsonProperty(propertyName: "placeholder")]
-        public string Placeholder { get; set; }
+        [JsonPropertyName("placeholder")]
+        public string? Placeholder { get; set; }
 
         /// <summary>
         /// Allows you to add instructions for the content managers while entering values for a field. The instructional text appears below the field.
         /// </summary>
-        [JsonProperty(propertyName: "instruction")]
-        public string Instruction { get; set; }
+        [JsonPropertyName("instruction")]
+        public string? Instruction { get; set; }
 
         /// <summary>
         /// Allows you to set single or multiple reference to Reference field.
         /// </summary>
-        [JsonProperty(propertyName: "ref_multiple")]
+        [JsonPropertyName("ref_multiple")]
         public bool RefMultiple { get; set; }
 
         /// <summary>
         /// When true, the field is a JSON Rich Text Editor (JRTE).
         /// </summary>
-        [JsonProperty(propertyName: "allow_json_rte")]
+        [JsonPropertyName("allow_json_rte")]
         public bool? AllowJsonRte { get; set; }
 
         /// <summary>
         /// Allows embedding entries in the JSON RTE / rich text configuration.
         /// </summary>
-        [JsonProperty(propertyName: "embed_entry")]
+        [JsonPropertyName("embed_entry")]
         public bool? EmbedEntry { get; set; }
 
     }
@@ -99,7 +101,7 @@ public class FileFieldMetadata: FieldMetadata
         /// <summary>
         /// Allows you to set single or multiple reference to Reference field.
         /// </summary>
-        [JsonProperty(propertyName: "image")]
+        [JsonPropertyName("image")]
         public bool AllowOnlyImage { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/FieldRules.cs b/Contentstack.Management.Core/Models/Fields/FieldRules.cs
index 0b0318e..1c55464 100644
--- a/Contentstack.Management.Core/Models/Fields/FieldRules.cs
+++ b/Contentstack.Management.Core/Models/Fields/FieldRules.cs
@@ -1,36 +1,36 @@
 using System;
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
     public class FieldRules
     {
-        [JsonProperty(propertyName: "match_type")]
-        public string MatchType { get; set; }
-        [JsonProperty(propertyName: "actions")]
-        public List<Action> Actions { get; set; }
-        [JsonProperty(propertyName: "conditions")]
-        public List<Condition> conditions { get; set; }
+        [JsonPropertyName("match_type")]
+        public string? MatchType { get; set; }
+        [JsonPropertyName("actions")]
+        public List<Action>? Actions { get; set; }
+        [JsonPropertyName("conditions")]
+        public List<Condition>? conditions { get; set; }
     }
 
     public class Action
     {
-        [JsonProperty(propertyName: "action")]
-        public string state { get; set; }
-        [JsonProperty(propertyName: "target_field")]
-        public string TargetField { get; set; }
+        [JsonPropertyName("action")]
+        public string? state { get; set; }
+        [JsonPropertyName("target_field")]
+        public string? TargetField { get; set; }
     }
 
     public class Condition
     {
-        [JsonProperty(propertyName: "dataType")]
-        public string DataType { get; set; }
-        [JsonProperty(propertyName: "operand_field")]
-        public string OperandField { get; set; }
-        [JsonProperty(propertyName: "operator")]
-        public string Operator { get; set; }
-        [JsonProperty(propertyName: "value")]
-        public string Value { get; set; }
+        [JsonPropertyName("dataType")]
+        public string? DataType { get; set; }
+        [JsonPropertyName("operand_field")]
+        public string? OperandField { get; set; }
+        [JsonPropertyName("operator")]
+        public string? Operator { get; set; }
+        [JsonPropertyName("value")]
+        public string? Value { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/FileField.cs b/Contentstack.Management.Core/Models/Fields/FileField.cs
index cedb73b..6b24cb1 100644
--- a/Contentstack.Management.Core/Models/Fields/FileField.cs
+++ b/Contentstack.Management.Core/Models/Fields/FileField.cs
@@ -1,34 +1,34 @@
 using System;
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
     public class FileField : Field
     {
-        [JsonProperty(propertyName: "extensions")]
+        [JsonPropertyName("extensions")]
         public List<string> Extensions { get; set; }
-        [JsonProperty(propertyName: "max")]
+        [JsonPropertyName("max")]
         public int? Maxsize { get; set; }
-        [JsonProperty(propertyName: "min")]
+        [JsonPropertyName("min")]
         public int? MinSize { get; set; }
         
     }
     public class ImageField : FileField
     {
-        [JsonProperty(propertyName: "dimension")]
+        [JsonPropertyName("dimension")]
         public Dimension Dimensions { get; set; }
         /// <summary>
         /// Allows you to enter additional data about a field. Also, you can add additional values under ‘field_metadata’.
         /// </summary>
-        [JsonProperty(propertyName: "field_metadata")]
+        [JsonPropertyName("field_metadata")]
         public new FileFieldMetadata FieldMetadata { get; set; }
     }
     public class Dimension
     {
-        [JsonProperty(propertyName: "height")]
+        [JsonPropertyName("height")]
         public Dictionary<string, int?> Height { get; set; }
-        [JsonProperty(propertyName: "width")]
+        [JsonPropertyName("width")]
         public Dictionary<string, int?> Width { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/GlobalFieldReference.cs b/Contentstack.Management.Core/Models/Fields/GlobalFieldReference.cs
index 05e7e49..b5181a2 100644
--- a/Contentstack.Management.Core/Models/Fields/GlobalFieldReference.cs
+++ b/Contentstack.Management.Core/Models/Fields/GlobalFieldReference.cs
@@ -1,5 +1,5 @@
 using System;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
@@ -12,30 +12,30 @@ public class GlobalFieldReference : Field
         /// <summary>
         /// The UID of the global field being referenced.
         /// </summary>
-        [JsonProperty(propertyName: "reference_to")]
+        [JsonPropertyName("reference_to")]
         public string ReferenceTo { get; set; }
 
         /// <summary>
         /// Determines if this field can accept multiple values.
         /// </summary>
-        [JsonProperty(propertyName: "multiple")]
+        [JsonPropertyName("multiple")]
         public new bool Multiple { get; set; }
 
         /// <summary>
         /// Determines if this field is mandatory.
         /// </summary>
-        [JsonProperty(propertyName: "mandatory")]
+        [JsonPropertyName("mandatory")]
         public new bool Mandatory { get; set; }
 
         /// <summary>
         /// Determines if this field value must be unique.
         /// </summary>
-        [JsonProperty(propertyName: "unique")]
+        [JsonPropertyName("unique")]
         public new bool Unique { get; set; }
         /// <summary>
         /// Determines if this field is non-localizable.
         /// </summary>
-        [JsonProperty(propertyName: "non_localizable")]
+        [JsonPropertyName("non_localizable")]
         public bool NonLocalizable { get; set; }
     }
 } 
diff --git a/Contentstack.Management.Core/Models/Fields/GroupField.cs b/Contentstack.Management.Core/Models/Fields/GroupField.cs
index f556696..0458972 100644
--- a/Contentstack.Management.Core/Models/Fields/GroupField.cs
+++ b/Contentstack.Management.Core/Models/Fields/GroupField.cs
@@ -1,16 +1,16 @@
 using System;
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
     public class GroupField : Field
     {
-        [JsonProperty(propertyName: "format")]
+        [JsonPropertyName("format")]
         public string Format { get; set; }
-        [JsonProperty(propertyName: "schema")]
+        [JsonPropertyName("schema")]
         public List<Field> Schema { get; set; }
-        [JsonProperty(propertyName: "max_instance")]
+        [JsonPropertyName("max_instance")]
         public int? MaxInstance { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/JsonField.cs b/Contentstack.Management.Core/Models/Fields/JsonField.cs
index fefd923..2188f8a 100644
--- a/Contentstack.Management.Core/Models/Fields/JsonField.cs
+++ b/Contentstack.Management.Core/Models/Fields/JsonField.cs
@@ -1,4 +1,5 @@
-using Newtonsoft.Json;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
@@ -7,7 +8,7 @@ namespace Contentstack.Management.Core.Models.Fields
     /// </summary>
     public class JsonField : TextboxField
     {
-        [JsonProperty(propertyName: "reference_to")]
-        public object ReferenceTo { get; set; }
+        [JsonPropertyName("reference_to")]
+        public JsonElement? ReferenceTo { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/ModularBlockField.cs b/Contentstack.Management.Core/Models/Fields/ModularBlockField.cs
index b177607..871d091 100644
--- a/Contentstack.Management.Core/Models/Fields/ModularBlockField.cs
+++ b/Contentstack.Management.Core/Models/Fields/ModularBlockField.cs
@@ -1,26 +1,26 @@
 using System;
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
     public class ModularBlockField : Field
     {
-        [JsonProperty(propertyName: "blocks")]
+        [JsonPropertyName("blocks")]
         public List<Block> blocks { get; set; }
     }
 
     public class Block
     {
-        [JsonProperty(propertyName: "title")]
+        [JsonPropertyName("title")]
         public string Title { get; set; }
-        [JsonProperty(propertyName: "uid")]
+        [JsonPropertyName("uid")]
         public string Uid { get; set; }
-        [JsonProperty(propertyName: "autoEdit")]
+        [JsonPropertyName("autoEdit")]
         public bool AutoEdit { get; set; }
-        [JsonProperty(propertyName: "blockType")]
+        [JsonPropertyName("blockType")]
         public bool BlockType { get; set; }
-        [JsonProperty(propertyName: "schema")]
+        [JsonPropertyName("schema")]
         public List<Field> Schema { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/NumberField.cs b/Contentstack.Management.Core/Models/Fields/NumberField.cs
index f67e92f..69b325a 100644
--- a/Contentstack.Management.Core/Models/Fields/NumberField.cs
+++ b/Contentstack.Management.Core/Models/Fields/NumberField.cs
@@ -1,4 +1,4 @@
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
@@ -7,10 +7,10 @@ namespace Contentstack.Management.Core.Models.Fields
     /// </summary>
     public class NumberField : Field
     {
-        [JsonProperty(propertyName: "min")]
+        [JsonPropertyName("min")]
         public int? Min { get; set; }
 
-        [JsonProperty(propertyName: "max")]
+        [JsonPropertyName("max")]
         public int? Max { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/ReferenceField.cs b/Contentstack.Management.Core/Models/Fields/ReferenceField.cs
index 135dc0b..569de5f 100644
--- a/Contentstack.Management.Core/Models/Fields/ReferenceField.cs
+++ b/Contentstack.Management.Core/Models/Fields/ReferenceField.cs
@@ -1,14 +1,15 @@
 using System;
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
     public class ReferenceField : Field
     {
-        [JsonProperty(propertyName: "reference_to")]
-        public object ReferenceTo { get; set; }
-        [JsonProperty(propertyName: "plugins")]
+        [JsonPropertyName("reference_to")]
+        public JsonElement? ReferenceTo { get; set; }
+        [JsonPropertyName("plugins")]
         public List<string> Plugins { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/SelectField.cs b/Contentstack.Management.Core/Models/Fields/SelectField.cs
index cfbdf14..ca03fe7 100644
--- a/Contentstack.Management.Core/Models/Fields/SelectField.cs
+++ b/Contentstack.Management.Core/Models/Fields/SelectField.cs
@@ -1,23 +1,24 @@
 using System;
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
     public class SelectField : Field
     {
-        [JsonProperty(propertyName: "enum")]
+        [JsonPropertyName("enum")]
         public SelectEnum Enum { get; set; }
 
     }
 
     public class SelectEnum
     {
-        [JsonProperty(propertyName: "advanced")]
+        [JsonPropertyName("advanced")]
         public bool Advanced { get; set; }
 
-        [JsonProperty(propertyName: "choices")]
-        public List<Dictionary<string, object>> Choices { get; set; }
+        [JsonPropertyName("choices")]
+        public List<Dictionary<string, JsonElement>> Choices { get; set; }
 
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/TaxonomyField.cs b/Contentstack.Management.Core/Models/Fields/TaxonomyField.cs
index c9698ef..f700e2b 100644
--- a/Contentstack.Management.Core/Models/Fields/TaxonomyField.cs
+++ b/Contentstack.Management.Core/Models/Fields/TaxonomyField.cs
@@ -1,5 +1,5 @@
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
@@ -8,7 +8,7 @@ namespace Contentstack.Management.Core.Models.Fields
     /// </summary>
     public class TaxonomyField : Field
     {
-        [JsonProperty(propertyName: "taxonomies")]
+        [JsonPropertyName("taxonomies")]
         public List<TaxonomyFieldBinding> Taxonomies { get; set; }
     }
 
@@ -17,19 +17,19 @@ public class TaxonomyField : Field
     /// </summary>
     public class TaxonomyFieldBinding
     {
-        [JsonProperty(propertyName: "taxonomy_uid")]
+        [JsonPropertyName("taxonomy_uid")]
         public string TaxonomyUid { get; set; }
 
-        [JsonProperty(propertyName: "max_terms")]
+        [JsonPropertyName("max_terms")]
         public int? MaxTerms { get; set; }
 
-        [JsonProperty(propertyName: "mandatory")]
+        [JsonPropertyName("mandatory")]
         public bool Mandatory { get; set; }
 
-        [JsonProperty(propertyName: "multiple")]
+        [JsonPropertyName("multiple")]
         public bool Multiple { get; set; }
 
-        [JsonProperty(propertyName: "non_localizable")]
+        [JsonPropertyName("non_localizable")]
         public bool NonLocalizable { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/Fields/TextboxField.cs b/Contentstack.Management.Core/Models/Fields/TextboxField.cs
index 7ad201b..cdd2fdc 100644
--- a/Contentstack.Management.Core/Models/Fields/TextboxField.cs
+++ b/Contentstack.Management.Core/Models/Fields/TextboxField.cs
@@ -1,16 +1,15 @@
 using System;
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models.Fields
 {
     public class TextboxField : Field
     {
-
-        [JsonProperty(propertyName: "format")]
+        [JsonPropertyName("format")]
         public string Format { get; set; }
 
-        [JsonProperty(propertyName: "error_messages")]
+        [JsonPropertyName("error_messages")]
         public Dictionary<string, string> ErrorMessages { get; set; }
     }
 }
diff --git a/Contentstack.Management.Core/Models/GlobalFieldRefs.cs b/Contentstack.Management.Core/Models/GlobalFieldRefs.cs
index ea9de95..dfe0088 100644
--- a/Contentstack.Management.Core/Models/GlobalFieldRefs.cs
+++ b/Contentstack.Management.Core/Models/GlobalFieldRefs.cs
@@ -1,5 +1,5 @@
 using System.Collections.Generic;
-using Newtonsoft.Json;
+using System.Text.Json.Serialization;
 
 namespace Contentstack.Management.Core.Models
 {
@@ -12,25 +12,25 @@ public class GlobalFieldRefs
         /// <summary>
         /// The UID of the referenced global field.
         /// </summary>
-        [JsonProperty(propertyName: "uid")]
-        public string Uid { get; set; }
+        [JsonPropertyName("uid")]
+        public string? Uid { get; set; }
 
         /// <summary>
         /// The number of times this global field is referenced in the schema.
         /// </summary>
-        [JsonProperty(propertyName: "occurrence_count")]
+        [JsonPropertyName("occurrence_count")]
         public int OccurrenceCount { get; set; }
 
         /// <summary>
         /// Indicates whether this is a child reference.
         /// </summary>
-        [JsonProperty(propertyName: "isChild")]
+        [JsonPropertyName("isChild")]
         public bool IsChild { get; set; }
 
         /// <summary>
         /// Array of paths where this global field reference occurs in the schema.
         /// </summary>
-        [JsonProperty(propertyName: "paths")]
-        public List<string> Paths { get; set; }
+        [JsonPropertyName("paths")]
+        public List<string>? Paths { get; set; }
     }
 } 
\ No newline at end of file
diff --git a/Contentstack.Management.Core/Models/Stack.cs b/Contentstack.Management.Core/Models/Stack.cs
index e400c80..636b1b8 100644
--- a/Contentstack.Management.Core/Models/Stack.cs
+++ b/Contentstack.Management.Core/Models/Stack.cs
@@ -604,8 +604,6 @@ public Locale Locale(string code = null)
         }
         */
 
-        /*
-        // The following resource methods are temporarily commented out as they reference excluded model types
         /// <summary>
         /// <see cref="Models.ContentType" /> defines the structure or schema of a page or a section of your web or mobile property.
         /// To create content for your application, you are required to first create a content type, and then create entries using the content type. 
@@ -619,13 +617,15 @@ public Locale Locale(string code = null)
         /// </code></pre>
         /// </example>
         /// <returns>The <see cref="Models.ContentType"/></returns>
-        public ContentType ContentType(string uid = null)
+        public ContentType ContentType(string? uid = null)
         {
             ThrowIfNotLoggedIn();
             ThrowIfAPIKeyEmpty();
 
             return new ContentType(this, uid);
         }
+
+        /*
         /// <summary>
         /// <see cref="Models.Asset"/> efer to all the media files (images, videos, PDFs, audio files, and so on) uploaded in your Contentstack repository for future use. 
         /// </summary>
diff --git a/Contentstack.Management.Core/Queryable/Query.cs b/Contentstack.Management.Core/Queryable/Query.cs
index e071188..32cc3ed 100644
--- a/Contentstack.Management.Core/Queryable/Query.cs
+++ b/Contentstack.Management.Core/Queryable/Query.cs
@@ -79,7 +79,6 @@ public Query IncludeCount()
             return this;
         }
 
-        /*
         /// <summary>
         /// The Find all object call fetches the list of all objects owned by a particular user account.
         /// </summary>
@@ -119,7 +118,6 @@ public Task<ContentstackResponse> FindAsync(ParameterCollection collection = nul
 
             return _stack.client.InvokeAsync<QueryService, ContentstackResponse>(service, false, _apiVersion);
         }
-        */
         #endregion
         #region Throw Error
 
diff --git a/Contentstack.Management.Core/Services/ContentstackService.cs b/Contentstack.Management.Core/Services/ContentstackService.cs
index 60a994c..f9b5d0b 100644
--- a/Contentstack.Management.Core/Services/ContentstackService.cs
+++ b/Contentstack.Management.Core/Services/ContentstackService.cs
@@ -29,7 +29,7 @@ internal class ContentstackService : IContentstackService
         #endregion
 
         #region Constructor
-        internal ContentstackService(JsonSerializerOptions serializerOptions, Models.Stack stack = null, ParameterCollection collection = null)
+        internal ContentstackService(JsonSerializerOptions serializerOptions, Contentstack.Management.Core.Models.Stack stack = null, ParameterCollection collection = null)
         {
             if (serializerOptions == null)
             {
diff --git a/Contentstack.Management.Core/Services/Models/CreateUpdateService.cs b/Contentstack.Management.Core/Services/Models/CreateUpdateService.cs
index b4530e6..ac1a7ac 100644
--- a/Contentstack.Management.Core/Services/Models/CreateUpdateService.cs
+++ b/Contentstack.Management.Core/Services/Models/CreateUpdateService.cs
@@ -1,8 +1,7 @@
 using System;
-using System.Globalization;
-using System.IO;
+using System.Collections.Generic;
+using System.Text.Json;
 using Contentstack.Management.Core.Queryable;
-using Newtonsoft.Json;
 using Contentstack.Management.Core.Utils;
 
 namespace Contentstack.Management.Core.Services.Models
@@ -13,8 +12,8 @@ internal class CreateUpdateService<T> : ContentstackService
         private readonly string fieldName;
         #region Internal
 
-        internal CreateUpdateService(JsonSerializer serializer, Core.Models.Stack stack, string resourcePath, T dataModel, string fieldName, string httpMethod = "POST", ParameterCollection collection = null)
-            : base(serializer, stack: stack, collection)
+        internal CreateUpdateService(Core.Models.Stack stack, string resourcePath, T dataModel, string fieldName, string httpMethod = "POST", ParameterCollection collection = null, JsonSerializerOptions stjOptions = null)
+            : base(stjOptions ?? stack?.client?.SerializerOptions ?? new JsonSerializerOptions(), stack: stack, collection: collection)
         {
             if (stack.APIKey == null)
             {
@@ -45,14 +44,13 @@ internal CreateUpdateService(JsonSerializer serializer, Core.Models.Stack stack,
 
         public override void ContentBody()
         {
-            using (StringWriter stringWriter = new StringWriter(CultureInfo.InvariantCulture))
+            var requestData = new Dictionary<string, object>
             {
-                JsonWriter writer = new JsonTextWriter(stringWriter);
+                { fieldName, _typedModel }
+            };
 
-                Serializer.Serialize(writer, _typedModel);
-                string snippet = $"{{\"{fieldName}\": {stringWriter.ToString()}}}";
-                this.ByteContent = System.Text.Encoding.UTF8.GetBytes(snippet); 
-            }
+            string jsonString = JsonSerializer.Serialize(requestData, SerializerOptions);
+            this.ByteContent = System.Text.Encoding.UTF8.GetBytes(jsonString);
         }
     }
 }
diff --git a/Contentstack.Management.Core/Services/Models/DeleteService.cs b/Contentstack.Management.Core/Services/Models/DeleteService.cs
index c0c4bec..715139b 100644
--- a/Contentstack.Management.Core/Services/Models/DeleteService.cs
+++ b/Contentstack.Management.Core/Services/Models/DeleteService.cs
@@ -1,8 +1,7 @@
 using System;
-using System.Globalization;
-using System.IO;
+using System.Collections.Generic;
+using System.Text.Json;
 using Contentstack.Management.Core.Queryable;
-using Newtonsoft.Json;
 using Contentstack.Management.Core.Utils;
 
 namespace Contentstack.Management.Core.Services.Models
@@ -12,8 +11,8 @@ internal class DeleteService<T>: ContentstackService
         internal string fieldName;
         internal T model;
 
-        internal DeleteService(JsonSerializer serializer, Core.Models.Stack stack, string resourcePath, string fieldName, T model, ParameterCollection collection = null)
-            : base(serializer, stack: stack, collection: collection)
+        internal DeleteService(Core.Models.Stack stack, string resourcePath, string fieldName, T model, ParameterCollection collection = null, JsonSerializerOptions stjOptions = null)
+            : base(stjOptions ?? stack?.client?.SerializerOptions ?? new JsonSerializerOptions(), stack: stack, collection: collection)
         {
             if (stack.APIKey == null)
             {
@@ -40,14 +39,13 @@ internal DeleteService(JsonSerializer serializer, Core.Models.Stack stack, strin
 
         public override void ContentBody()
         {
-            using (StringWriter stringWriter = new StringWriter(CultureInfo.InvariantCulture))
+            var requestData = new Dictionary<string, object>
             {
-                JsonWriter writer = new JsonTextWriter(stringWriter);
+                { fieldName, model }
+            };
 
-                Serializer.Serialize(writer, model);
-                string snippet = $"{{\"{fieldName}\": {stringWriter.ToString()}}}";
-                this.ByteContent = System.Text.Encoding.UTF8.GetBytes(snippet);
-            }
+            string jsonString = JsonSerializer.Serialize(requestData, SerializerOptions);
+            this.ByteContent = System.Text.Encoding.UTF8.GetBytes(jsonString);
         }
     }
 }
diff --git a/Contentstack.Management.Core/Services/Models/FetchDeleteService.cs b/Contentstack.Management.Core/Services/Models/FetchDeleteService.cs
index 8bd26bb..6ed5953 100644
--- a/Contentstack.Management.Core/Services/Models/FetchDeleteService.cs
+++ b/Contentstack.Management.Core/Services/Models/FetchDeleteService.cs
@@ -1,6 +1,6 @@
 using System;
+using System.Text.Json;
 using Contentstack.Management.Core.Queryable;
-using Newtonsoft.Json;
 using Contentstack.Management.Core.Utils;
 
 namespace Contentstack.Management.Core.Services.Models
@@ -9,8 +9,8 @@ internal class FetchDeleteService: ContentstackService
     {
         #region Internal
 
-        internal FetchDeleteService(JsonSerializer serializer, Core.Models.Stack stack, string resourcePath, string httpMethod = "GET", ParameterCollection collection = null)
-            : base(serializer, stack: stack, collection)
+        internal FetchDeleteService(Core.Models.Stack stack, string resourcePath, string httpMethod = "GET", ParameterCollection collection = null, JsonSerializerOptions stjOptions = null)
+            : base(stjOptions ?? stack?.client?.SerializerOptions ?? new JsonSerializerOptions(), stack: stack, collection: collection)
         {
             if (stack.APIKey == null)
             {
diff --git a/Contentstack.Management.Core/Services/QueryService.cs b/Contentstack.Management.Core/Services/QueryService.cs
index 751e7c4..fc60dcd 100644
--- a/Contentstack.Management.Core/Services/QueryService.cs
+++ b/Contentstack.Management.Core/Services/QueryService.cs
@@ -1,5 +1,5 @@
 using System;
-using Newtonsoft.Json;
+using System.Text.Json;
 using Contentstack.Management.Core.Queryable;
 using Contentstack.Management.Core.Utils;
 
@@ -10,7 +10,7 @@ internal class QueryService: ContentstackService
         #region Internal
 
         internal QueryService(Core.Models.Stack stack, ParameterCollection collection, string resourcePath)
-            : base(stack.client.serializer, stack, collection)
+            : base(stack.client.SerializerOptions, stack, collection)
         {
             if (string.IsNullOrEmpty(resourcePath))
             {
diff --git a/Contentstack.Management.Core/Utils/FieldJsonConverter.cs b/Contentstack.Management.Core/Utils/FieldJsonConverter.cs
index 6d70e6a..f92c15f 100644
--- a/Contentstack.Management.Core/Utils/FieldJsonConverter.cs
+++ b/Contentstack.Management.Core/Utils/FieldJsonConverter.cs
@@ -36,6 +36,7 @@ public override void Write(Utf8JsonWriter writer, Field value, JsonSerializerOpt
 
         private static Type ResolveConcreteType(JsonElement jo)
         {
+            // Check for extension fields first
             var extensionUid = jo.TryGetProperty("extension_uid", out var ext) ? ext.GetString() : null;
             if (!string.IsNullOrEmpty(extensionUid))
                 return typeof(ExtensionField);
diff --git a/Contentstack.Management.Core/contentstack.management.core.csproj b/Contentstack.Management.Core/contentstack.management.core.csproj
index ebd9fef..c1efd89 100644
--- a/Contentstack.Management.Core/contentstack.management.core.csproj
+++ b/Contentstack.Management.Core/contentstack.management.core.csproj
@@ -84,10 +84,10 @@
     <Compile Remove="Models\Asset.cs" />
     <Compile Remove="Models\AssetModel.cs" />
     <Compile Remove="Models\AuditLog.cs" />
-    <Compile Remove="Models\BaseModel.cs" />
+    <!-- BaseModel.cs - RE-ENABLED for ContentType -->
     <!-- BulkOperation.cs - RE-ENABLED -->
-    <Compile Remove="Models\ContentModelling.cs" />
-    <Compile Remove="Models\ContentType.cs" />
+    <!-- ContentModelling.cs - RE-ENABLED for ContentType -->
+    <!-- ContentType.cs - RE-ENABLED -->
     <Compile Remove="Models\Entry.cs" />
     <Compile Remove="Models\EntryVariant.cs" />
     <Compile Remove="Models\Environment.cs" />
@@ -110,13 +110,35 @@
     <Compile Remove="Models\Webhook.cs" />
     <Compile Remove="Models\Workflow.cs" />
     <Compile Remove="Models\CustomExtension\**\*.cs" />
-    <Compile Remove="Models\Fields\**\*.cs" />
+    <!-- Re-enable core Field models for ContentType support -->
+    <!-- Phase 1 field types - RE-ENABLED and converted to STJ -->
+    <!-- DateField.cs, NumberField.cs, TextboxField.cs, ExtensionField.cs, ReferenceField.cs, GlobalFieldReference.cs - RE-ENABLED -->
+    <!-- Phase 2 field types - RE-ENABLED and converted to STJ -->
+    <!-- FileField.cs (includes ImageField and Dimension), JsonField.cs - RE-ENABLED -->
+    <!-- Phase 3 field types - RE-ENABLED and converted to STJ -->
+    <!-- SelectField.cs (includes SelectEnum), TaxonomyField.cs (includes TaxonomyFieldBinding) - RE-ENABLED -->
+    <!-- Phase 4 field types - RE-ENABLED and converted to STJ -->
+    <!-- GroupField.cs, ModularBlockField.cs (includes Block) - RE-ENABLED -->
+    <!-- FieldMetadata.cs, Field.cs, FieldRules.cs - RE-ENABLED for ContentType -->
     <Compile Remove="Models\Token\**\*.cs" />
     
     <!-- Re-enable core services for Client, User, Organization, Stack modules -->
     <Compile Remove="Services\DeleteReleaseItemService.cs" />
-    <Compile Remove="Services\QueryService.cs" />
-    <Compile Remove="Services\Models\**\*.cs" />
+    <!-- QueryService.cs - RE-ENABLED for ContentType listing -->
+    <!-- Re-enable essential model services for ContentType -->
+    <Compile Remove="Services\Models\GlobalFieldService.cs" />
+    <Compile Remove="Services\Models\GlobalFieldFetchDeleteService.cs" />
+    <Compile Remove="Services\Models\ImportExportService.cs" />
+    <Compile Remove="Services\Models\LocaleService.cs" />
+    <Compile Remove="Services\Models\LocalizationService.cs" />
+    <Compile Remove="Services\Models\FetchReferencesService.cs" />
+    <Compile Remove="Services\Models\CreateUpdateFolderService.cs" />
+    <Compile Remove="Services\Models\UploadService.cs" />
+    <Compile Remove="Services\Models\VariantContentTypeLinkService.cs" />
+    <Compile Remove="Services\Models\PublishUnpublishService.cs" />
+    <!-- Exclude Versioning services -->
+    <Compile Remove="Services\Models\Versioning\**\*.cs" />
+    <!-- CreateUpdateService, FetchDeleteService, DeleteService - RE-ENABLED for ContentType -->
     <Compile Remove="Services\OAuth\**\*.cs" />
     <!-- StackOwnershipService.cs, StackShareService.cs, UpdateUserRoleService.cs - RE-ENABLED -->
     <!-- OrgRoles.cs - RE-ENABLED -->
@@ -127,8 +149,7 @@
     <!-- Keep OAuth handler excluded -->
     <Compile Remove="OAuthHandler.cs" />
     
-    <!-- Keep FieldJsonConverter excluded -->
-    <Compile Remove="Utils\FieldJsonConverter.cs" />
+    <!-- FieldJsonConverter.cs - RE-ENABLED for ContentType Field support -->
     
     <!-- Stack.cs - RE-ENABLED -->
     
diff --git a/Directory.Build.props b/Directory.Build.props
index 2ad39e3..1945233 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -1,5 +1,5 @@
 <Project>
   <PropertyGroup>
-    <Version>1.0.0-beta.2</Version>
+    <Version>1.0.0-beta.3</Version>
   </PropertyGroup>
 </Project>