This happened to someone at my company and we believe it was caused by their Apple ID being an old @me.com email address. After they updated their email, signed out and back in to iCloud with their Apple ID on their device, they were able to use Sign in with Apple without problems. I mentioned this to the reviewer but all they told me was that they are using a "valid iCloud account." I'm going to try referring them to this thread next. The specific error that comes back from the ASAuthorizationControllerDelegate's didCompleteWithError callback is "canceled." More on "canceled" error: https://developer.apple.com/documentation/authenticationservices/asauthorizationerror/code/canceled More on @me.com email address: https://support.apple.com/en-us/HT201771