diff --git a/packages/javascript-sdk/src/fr-webauthn/fr-webauthn.test.ts b/packages/javascript-sdk/src/fr-webauthn/fr-webauthn.test.ts
index bfb73d20..15bce073 100644
--- a/packages/javascript-sdk/src/fr-webauthn/fr-webauthn.test.ts
+++ b/packages/javascript-sdk/src/fr-webauthn/fr-webauthn.test.ts
@@ -210,4 +210,38 @@ describe('Test FRWebAuthn class with Conditional UI', () => {
       }),
     );
   });
+
+  it('should throw NotSupportedError if WebAuthn is not supported', async () => {
+    // Mock WebAuthn not supported
+    const spy = vi.spyOn(FRWebAuthn, 'isWebAuthnSupported').mockReturnValue(false);
+
+    await expect(FRWebAuthn.getRegistrationCredential({} as any)).rejects.toThrow(
+      'PublicKeyCredential not supported by this browser',
+    );
+
+    spy.mockRestore();
+  });
+
+  it('should correctly convert _allowCredentials id to Int8Array', () => {
+    const metadata: any = {
+      _action: 'webauthn_authentication',
+      challenge: 'JEisuqkVMhI490jM0/iEgrRz+j94OoGc7gdY4gYicSk=',
+      relyingPartyId: '',
+      _allowCredentials: [
+        {
+          type: 'public-key',
+          id: [1, 2, 3, 4],
+          transports: ['usb'],
+        },
+      ],
+      timeout: 60000,
+    };
+
+    const publicKey = FRWebAuthn.createAuthenticationPublicKey(metadata);
+
+    expect(publicKey.allowCredentials).toBeDefined();
+    expect(publicKey.allowCredentials![0].id).toBeInstanceOf(Int8Array);
+    const idArray = publicKey.allowCredentials![0].id as Int8Array;
+    expect(Array.from(idArray)).toEqual([1, 2, 3, 4]);
+  });
 });
diff --git a/packages/javascript-sdk/src/fr-webauthn/index.ts b/packages/javascript-sdk/src/fr-webauthn/index.ts
index d07a3072..ee1ec5ec 100644
--- a/packages/javascript-sdk/src/fr-webauthn/index.ts
+++ b/packages/javascript-sdk/src/fr-webauthn/index.ts
@@ -469,7 +469,7 @@ abstract class FRWebAuthn {
     options: PublicKeyCredentialCreationOptions,
   ): Promise<PublicKeyCredential | null> {
     // Feature check before we attempt registering a device
-    if (this.isWebAuthnSupported()) {
+    if (!this.isWebAuthnSupported()) {
       const e = new Error('PublicKeyCredential not supported by this browser');
       e.name = WebAuthnOutcomeType.NotSupportedError;
       throw e;
@@ -534,7 +534,14 @@ abstract class FRWebAuthn {
     // Use the structured _allowCredentials if available, otherwise parse the string format
     let allowCredentialsValue: PublicKeyCredentialDescriptor[] | undefined;
     if (_allowCredentials && Array.isArray(_allowCredentials)) {
-      allowCredentialsValue = _allowCredentials;
+      // The incoming _allowCredentials entries have an `id` property of type `Array`, which is rejected by `navigator.credentials.get()`.
+      // Converting it to a TypedArray here to meet the spec (https://developer.mozilla.org/en-US/docs/Web/API/PublicKeyCredentialRequestOptions#id).
+      allowCredentialsValue = _allowCredentials.map((cred) => {
+        return {
+          ...cred,
+          id: new Int8Array(cred.id as unknown as number[]),
+        };
+      });
     } else {
       allowCredentialsValue = parseCredentials(allowCredentials || acceptableCredentials || '');
     }