React Native Google Sign-In Fix

I'm seeking an experienced React Native developer to fix a Google Authentication issue in our app (GitHub Repo). Firebase Authentication is integrated, and the Google Sign-In package is installed, but users encounter errors during login.

Key Tasks:
- Review current Google Sign-In implementation
- Debug OAuth/Firebase configuration issues
- Ensure sign-in functionality on both iOS and Android
- Provide a tested fix along with brief documentation

Ideal Skills & Experience:
- Strong expertise in React Native and Firebase Authentication
- Deep understanding of OAuth 2.0, Google APIs, and mobile sign-in flows
- Familiarity with platform-specific setups such as Gradle and GoogleService-Info.plist

The fix is needed within 3 to 5 days.