To Solve Undefined class ‘FirebaseUser’ just use User instead of FirebaseUser because after the new update of package firebase_auth, the class FirebaseUser was changed to User , and the class AuthResult was changed to UserCredentail. Therefore change FirebaseUser to User.
Read moreIs Firebase Auth really free?
All other Firebase Auth features are no-cost on all plans . Prices are per successful verification. On the Blaze plan, Phone Authentication provides a no-cost tier. The first 10K verifications for both instances (USA, Canada, and India and All other countries) are provided at no cost each month.
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