Firebase Mobile App Debugging

I need an experienced Firebase Backend Developer to quickly identify and fix a data fetching issue in our mobile app.

The app is supposed to use both Firestore and Realtime Database. We have the APK build file and complete source code.

Requirements:
- Identify the root cause of the issue
- Fix the data connection problem so that the app can fetch data from Firebase

Ideal Skills:
- Proficient in Firebase (Firestore and Realtime Database)
- Experience with mobile app debugging
- Strong problem-solving skills
- Familiarity with reading and analyzing code

Please ensure you have relevant experience and can work efficiently to resolve this issue.