Thank you for your kind words ❤

Here are some suggestions:

1) Try another attestation provider (there is an open bug report with Play Integrity, maybe some others don't work, too. I tried with SafetyNet and it worked).

2) Check your debug output of your Flutter app. There might be hints about what is not working. Do you get an error when making requests to Firebase?

3) Is your Flutter Firebase initialization code working without errors?

4) Is your Flutter app connected to the correct Firebase project? I had this problem once when working with multiple projects and my app accessed the wrong one.

Maybe this helps to solve your issue.