Flutter and Firebase Mobile App Authentication Fix: Login and Registration Issues

I already have a mobile app developed using Flutter and Firebase, but I am currently facing issues with the login and registration features.

I am looking for an experienced mobile developer who can review the existing app, identify the cause of the errors, and fix the authentication flow properly.

Main tasks:

・Review the current Flutter/Firebase authentication setup
・Fix login errors
・Fix user registration errors
・Check Firebase configuration and authentication rules
・Test the login and registration flow after fixing
・Make sure the app works correctly on Android and/or iOS

Requirements:

・Strong experience with Flutter
・Experience with Firebase Authentication
・Ability to debug existing code
・Clean and reliable communication
・Ability to explain what was fixed

The app is already developed, so this is not a full app development project. The main goal is to fix the current authentication issues and make the login/register process work correctly.