Flutter Firebase Phone Authentication OTP SMS not received (codeSent callback triggered)

[gopalbhowmik7865-source]

Hi everyone,

I'm building a Flutter app called QuickDrop.

Problem:
Firebase Phone Authentication is not sending OTP SMS.

Current status:

• Phone Authentication is enabled.
• SHA-1 and SHA-256 are added.
• google-services.json is downloaded from Firebase.
• Package name matches.
• Real Android device is used.
• verifyPhoneNumber() reaches the codeSent callback successfully.
• But no OTP SMS is received.

I also noticed:

• Sometimes I get build errors related to google-services.json.
• I have already checked Firebase configuration multiple times.

Repository:
https://github.com/gopalbhowmik7865-source/QuickDrop

Can someone help me identify the root cause?
Additional information:

• Flutter: (run flutter --version)
• Firebase Auth: Enabled
• Android device: Real device (not emulator)
• Android version: 12
• I can provide the complete project if needed.

[abidiahmedcom]

Hi @gopalbhowmik7865-source,

Your debug logs reveal the real issue. The key errors are:

1. API_KEY_ANDROID_APP_BLOCKED
2. Play Integrity checks, and reCAPTCHA checks were unsuccessful
3. Error getting App Check token → No AppCheckProvider installed

What's happening:
Firebase is trying to send the SMS, but Google cannot verify your Android app. This is not a Flutter code issue, it's a Firebase/Google Cloud configuration issue.

Check in this order:

1. API Key restrictions
API_KEY_ANDROID_APP_BLOCKED means your API key is blocking your Android app.
Go to Google Cloud Console → APIs & Services → Credentials, find the API key used by your Android app, and check Application restrictions. Make sure your Firebase Android app is allowed.

2. SHA fingerprints
Even though you added them, verify they're correct:

keytool -list -v -alias androiddebugkey -keystore ~/.android/debug.keystore -storepass android

Add both SHA-1 and SHA-256 to Firebase Console → Project Settings → Your Android App → SHA certificate fingerprints.

3. google-services.json
Download a fresh copy from Firebase Console and replace android/app/google-services.json. Then run:

flutter clean
flutter pub get
flutter run

4. App Check
The error Error getting App Check token → No AppCheckProvider installed suggests App Check is expected but not configured. Either set up an App Check provider or disable App Check for Phone Auth in Firebase Console.

Quick test: Add your phone number as a test number in Firebase Console → Authentication → Sign-in method → Phone → Phone numbers for testing. This bypasses Play Integrity and reCAPTCHA entirely. If this works, the issue is definitely configuration, not code.