Hello ppinkney, We also got that response only when the reviewers tried to login. We tested both with on iPhones, iPads and in the emulator and we cannot reproduce the error: {"error":"invalid_grant","error_description":"The code has already been used."} Our review process already failed 4 times. We also opened a support ticket.

The problem is solved for us. We deleted the keys and generated new keys and the login works.

I can confirm we have the same problem after deleting and creating a new service id. Even more strange, the app works with the old (deleted) service id passed as client_id to apple. It should not work with the old (deleted) service id!