How I fixed Firebase permission-denied after enabling App Check in React Native Android

If your React Native app signs users in correctly with Firebase Auth, but Firestore suddenly starts throwing: permission-denied ...especially after enabling Firebase App Check with Play Integrity on Android, this can be very misleading. That was exactly the situation I ran into. At first, it looked like a Firestore rules issue. But the rules were fine. Auth was also working. The real problem was deeper: App Check was enabled, but it was not actually installed and initialized correctly on the native Android side. This post is a practical breakdown of what happened, what made this error confusing, and what I would check first if I hit it again. * The symptom * The setup looked normal on the surface: Firebase Auth was working the user was signed in Firestore rules looked correct the app worked differently depending on environment after enabling App Check / Play Integrity, Firestore requests started failing with permission-denied That error pushes me toward checking security rules first, w