Some of you guys might be facing this issue in FlutterFlow CMS, even when you have done it correctly, you will still be having this error there.
You can follow this as such.
Make sure "Email Sign-In" is turned on for your Firebase project. Click the pencil icon to Enable it.
Delete the firebase@flutterflow.io User from Authentication -> Users (if it already exists)
This account will be recreated by Flutterflow once you go to CMS again.
That's it. You will be able to manage your Firebase content directly in FlutterFlow.
Update: If the following steps still don't work out for you.
Try these suggestions from community members below :
Reconnect your Firebase Project
Regenerating Config Files from Firebase.
Redeploy your Firebase Rules
Then try re-applying the above solution.
