Hello Apple engineers, We are investigating an unresolved native Sign in with Apple failure in Rankids. Feedback FB24763387 contains the private reproduction details and Accounts/AuthKit sysdiagnose. The native Apple sheet displays "Sign in not complete" after biometric authentication and before returning any authorization credential. Both Share My Email and Hide My Email fail. We reproduced it on an iPhone and an iPad, while the same account can use Sign in with Apple in unrelated apps. The diagnostic build is TestFlight 1.0.9 (5). Accounts/AuthKit diagnostics show successful biometric authentication followed by AKAuthenticationServerError -24000 / "Invalid client.". The app receives ASAuthorizationError 1001 after the failed sheet is manually dismissed; that cancellation is not the original failure. No identity token reaches our app, so no backend token exchange takes place. The App ID capability was checked as enabled/Primary. The diagnostic binary and installed-device logs show the expected app/team identifiers and the Default Sign in with Apple entitlement. The app uses Expo Apple Authentication; we have not yet reproduced this in a separate minimal native Xcode project and are not claiming a confirmed server-side root cause. Could an Apple engineer advise whether the existing private diagnostics are sufficient to investigate the client rejection, and what additional evidence would distinguish an app configuration issue from an Apple-side registration issue? The code-level request form requires a focused Xcode project; guidance on the appropriate route for investigating the affected app registration would be appreciated. The production app currently uses email/password sign-in while we investigate. Account identifiers and full diagnostic files will remain in the private support channels. Thank you.