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FCM_TOKEN_FIX_REPORT.md

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FCM Token Fix - Bug Report and Resolution

Date: January 25, 2026 Issue: Signal creators not receiving comment notifications Status: ✅ RESOLVED

Problem Summary

Signal creators were not receiving push notifications when other users commented on their signals. Investigation revealed that FCM tokens were not being saved to Firestore after user authentication.

Root Causes

1. FCM Tokens Not Saved After Authentication

Location: lib/src/services/auth_service.dart

FCM tokens were only saved during the initial notification setup, but not after user authentication flows. This meant:

  • Anonymous users who upgraded to authenticated accounts had no FCM tokens saved
  • Users signing in with email/password had no FCM tokens saved
  • Users signing in with Google OAuth had no FCM tokens saved

2. Missing Token Update After Permission Grant

Location: lib/src/services/notification_service.dart

The completeInitialization() method did not update FCM tokens after permissions were granted, missing users who already had permissions before app launch.

Solution Implemented

Fix 1: Save FCM Tokens After All Auth Flows

File: lib/src/services/auth_service.dart Lines: 165-223

Added await NotificationService().onUserLogin() calls in three locations:

  1. After anonymous sign-in conversion (line 172-176)
final result = await _auth.signInWithCredential(credential);
if (result.user != null) {
  try {
    await NotificationService().onUserLogin();
  } catch (e) {
    debugPrint('Failed to save FCM token after sign-in: $e');
  }
}
  1. After successful account linking (line 181-186)
case LinkResult.linked:
  try {
    await NotificationService().onUserLogin();
  } catch (e) {
    debugPrint('Failed to save FCM token after linking: $e');
  }
  return _auth.currentUser;
  1. After merge during account conflict (line 195-200)
if (existingUser != null) {
  await mergeAnonymousIntoExisting(anonymousUid, existingUser.uid);
  try {
    await NotificationService().onUserLogin();
  } catch (e) {
    debugPrint('Failed to save FCM token after merge: $e');
  }
}

Fix 2: Update FCM Token After Permission Grant

File: lib/src/services/notification_service.dart Lines: 82-93

Added token update at end of completeInitialization():

// Listen for token refresh
_messaging.onTokenRefresh.listen((token) {
  _saveFcmTokenToFirestore(token);
});

_isFullyInitialized = true;

// Get and save the current FCM token
// This ensures token is saved for users who already have permissions
await _updateFcmToken();

Test Results

Test Setup

  • Android Device: Samsung SM-X205 (R9PW402KZEE)
  • iOS Device: iPad (6c602c36e83e447ac48c4477f18fac43d1e00175)
  • Test Signal: "FCM Token Test"
  • Date: January 25, 2026

Test Execution

  1. Signal Creation (18:37)

    • Created signal on Android device
    • Signal appeared on map
    • Creator auto-subscribed to signal

  2. Comment Submission (19:36)

    • Added comment from iPad: "Testing FCM notification from iPad"
    • Comment saved successfully to Firestore
    • Cloud Function triggered

  3. Cloud Function Logs (17:36:19 UTC)

onCommentCreated triggered for signal: K0KhJXEDmFrgA1nAieKs
Comment text: Testing FCM notification from iPad
Signal title: FCM Token Test
Found subscribed users: 2
Processing user: PnCYysuA1tbvSK25uMzHcWmoeM23
  User has FCM tokens: 1
  Adding user to notification list
Processing user: zkaEO07MMQWYEAxkHMjC8V6bpa63
  User has FCM tokens: 0
  Skipping comment author
Total users to notify: 1
Notifications sent successfully
  1. Notification Delivery ✅
    • Android received notification at 19:36
    • Title: "New comment on: FCM Token Test"
    • Body: "Testing FCM notification from iPad"

Verification

✅ FCM tokens saved after authentication ✅ Signal creators auto-subscribed to their signals ✅ Comment notifications delivered to creators ✅ Cloud Function correctly filters comment authors ✅ Cross-device notification working (iOS → Android)

Files Modified

  1. /lib/src/services/auth_service.dart - Added FCM token saving after auth flows
  2. /lib/src/services/notification_service.dart - Added token update after permission grant
  3. /functions/src/index.ts - Enhanced logging (debugging only, no functional changes)

Related Code

Auto-subscribe logic (already implemented in previous session): lib/src/widgets/map_page.dart:636-644

// Subscribe creator to their own signal for notifications
await FirebaseFirestore.instance.collection('users').doc(FirebaseAuth.instance.currentUser!.uid).set(
  {
    'signalSubscriptions': FieldValue.arrayUnion([docRef.id]),
  },
  SetOptions(merge: true),
);

Notes

  • The proximity notification "New signal nearby!" received at 18:37 proves the FCM infrastructure was working
  • The missing piece was FCM token persistence after authentication
  • Cloud Function logs show proper filtering: author had 0 tokens (iPad user didn't grant permissions), creator had 1 token

Future Improvements

Consider moving subscription logic to Cloud Functions for better consistency (noted in TODO at map_page.dart:635).