There are apps that use Firebase Google authentication. When I get the request for this app, I copy the project and change the package name, connect the app to the FireBase with that person's Google account, and provide the app. However, I recently created the app in exactly the same way, but I get an error (ApiException: 12500).
I also changed the SHA-1 key value and confirmed support email, but the same problem is repeated.
Did this error occur because duplicate SHA-1 key values were used? However, changing the SHA-1 key value does not solve the problem.