auth/invalid-credential
what this Firebase error means
How it shows up
FirebaseError: Firebase: Error (auth/invalid-credential).
What it means
The sign-in details were not accepted. For email and password sign-in, Firebase returns this code for a wrong email or password when email enumeration protection is on.
The usual cause in an AI-built app
Often the person first signed up with Google, so the account has no password, and the AI-built login form tries an email and password sign-in that can never match.
Check this first
In the Firebase console, find the email under Authentication, Users and check which sign-in providers the account has.