Please follow the steps below, then return to Famm and try "Sign in with Apple".
- So to "Settings" on your iPhone
- Tap your Apple ID on the top of the Settings
- Tap "Password & Security"
- Tap "Apple ID Logins"
- Tap "Famm"
- Tap "Stop using Apple ID"
- Close Settings, and return to Famm
- Retry "Sign in with Apple"