This Firebase Cloud Messaging error occurs when a registration token (FCM token) is being used with a different sender ID than the one it was originally created for. The token is permanently tied to its original sender ID and cannot be used with other Firebase projects.
The "messaging/SENDER_ID_MISMATCH" error in Firebase Cloud Messaging (FCM) indicates that you're trying to use a registration token with a Firebase project that differs from the one the token was originally generated for. Each FCM registration token is cryptographically tied to a specific sender ID (which corresponds to a Firebase project) at creation time. When a mobile app registers with FCM, it receives a token that's uniquely associated with: 1. The specific Firebase project (identified by its sender ID) 2. The specific app instance/device 3. The specific app package/bundle identifier This binding is permanent - tokens cannot be transferred between Firebase projects. If you attempt to send a message using a token from Project A through Project B's credentials, FCM rejects it with this error to prevent cross-project message delivery. This error commonly occurs during development when switching between Firebase projects, or in production when migrating apps between projects without proper token refresh.
Check that your server-side Firebase Admin SDK is configured with the correct project credentials that match where the tokens were generated:
// Initialize Firebase Admin SDK with correct service account
const admin = require('firebase-admin');
// Method 1: Using environment variable (recommended for production)
admin.initializeApp({
credential: admin.credential.applicationDefault(),
projectId: 'your-correct-project-id' // Verify this matches token source
});
// Method 2: Using service account JSON file
const serviceAccount = require('./path/to/serviceAccountKey.json');
admin.initializeApp({
credential: admin.credential.cert(serviceAccount)
});
// Verify the project ID
console.log('Current project ID:', admin.app().options.projectId);
// Compare with where tokens were generated:
// - Check client app's google-services.json (Android)
// - Check client app's GoogleService-Info.plist (iOS)
// - Check web app's firebase configEnsure the project ID in your server configuration matches the project where client apps are registered.
When switching Firebase projects, you must refresh tokens on all client devices:
// On client (Android/iOS/Web), get a fresh token
// Example for web:
import { getMessaging, getToken } from "firebase/messaging";
const messaging = getMessaging();
// Request permission and get token
async function requestPermissionAndGetToken() {
try {
const permission = await Notification.requestPermission();
if (permission === 'granted') {
const token = await getToken(messaging, {
vapidKey: 'YOUR_VAPID_KEY' // From Firebase Console > Cloud Messaging
});
console.log('New FCM token:', token);
// Send this new token to your server
await sendTokenToServer(token);
return token;
}
} catch (error) {
console.error('Error getting token:', error);
}
}
// For existing apps, you can also listen for token refresh:
import { onTokenRefresh } from "firebase/messaging";
onTokenRefresh(messaging, () => {
getToken(messaging).then((refreshedToken) => {
console.log('Token refreshed:', refreshedToken);
sendTokenToServer(refreshedToken);
});
});Old tokens from the previous project will continue to fail with SENDER_ID_MISMATCH.
Verify the client app is configured for the correct Firebase project:
For Android (google-services.json):
{
"project_info": {
"project_number": "123456789012", // This is the sender ID
"project_id": "your-project-id",
"storage_bucket": "your-project-id.appspot.com"
},
"client": [...],
"configuration_version": "1"
}For iOS (GoogleService-Info.plist):
<key>PROJECT_ID</key>
<string>your-project-id</string>
<key>GOOGLE_APP_ID</key>
<string>1:123456789012:ios:abc123def456</string>For web (firebase config):
const firebaseConfig = {
apiKey: "your-api-key",
authDomain: "your-project-id.firebaseapp.com",
projectId: "your-project-id", // Must match server project
storageBucket: "your-project-id.appspot.com",
messagingSenderId: "123456789012", // This is the sender ID
appId: "1:123456789012:web:abc123def456"
};The messagingSenderId (also called project number) must match between client and server.
Add server-side validation to detect and handle mismatched tokens:
const admin = require('firebase-admin');
async function sendMessageWithValidation(token, message) {
try {
const response = await admin.messaging().send({
token: token,
notification: {
title: message.title,
body: message.body
}
});
console.log('Message sent successfully:', response);
return { success: true, response };
} catch (error) {
console.error('Error sending message:', error.message);
// Check for SENDER_ID_MISMATCH specifically
if (error.code === 'messaging/sender-id-mismatch' ||
error.message.includes('SENDER_ID_MISMATCH')) {
console.log('Token belongs to different project:', token);
// Remove this token from your database
await removeInvalidTokenFromDatabase(token);
// Optionally notify client to refresh token
await notifyClientToRefreshToken(token);
return {
success: false,
error: 'SENDER_ID_MISMATCH',
action: 'token_removed'
};
}
// Handle other errors
return { success: false, error: error.message };
}
}
// Helper function to remove invalid token
async function removeInvalidTokenFromDatabase(token) {
// Remove from your database/Redis cache
await db.tokens.deleteOne({ token: token });
console.log('Removed invalid token from database');
}
// Helper to notify client (if you have a way to communicate back)
async function notifyClientToRefreshToken(token) {
// Could use other channels like WebSockets, database flags, etc.
// This depends on your app architecture
}Use Firebase Admin SDK to validate tokens before sending messages:
const admin = require('firebase-admin');
async function validateToken(token) {
try {
// This will fail if token is from different project
const info = await admin.messaging().getRegistrationTokenInfo(token);
console.log('Token is valid:', {
projectId: info.projectId,
appId: info.appId,
platform: info.platform,
token: token.substring(0, 20) + '...' // Log partial for security
});
return { valid: true, info };
} catch (error) {
if (error.code === 'messaging/sender-id-mismatch') {
console.log('Token belongs to different project');
return { valid: false, reason: 'SENDER_ID_MISMATCH' };
}
console.error('Token validation error:', error.message);
return { valid: false, reason: error.code };
}
}
// Usage: Validate tokens before storing or using them
const token = 'your-fcm-token';
const validation = await validateToken(token);
if (!validation.valid) {
if (validation.reason === 'SENDER_ID_MISMATCH') {
console.log('Do not store this token - it's from wrong project');
// Prompt user to re-register for notifications
}
}This proactive validation helps prevent storing invalid tokens.
If migrating between Firebase projects, follow this sequence:
1. Prepare new project:
- Create new Firebase project
- Configure Cloud Messaging
- Get new VAPID key (for web) and configuration files
2. Update client apps gradually:
- Release app update with new Firebase configuration
- Implement dual-token support during transition
- Listen for new tokens and send to server
3. Server-side transition:
// Support both old and new projects during migration
const adminOld = require('firebase-admin');
const adminNew = require('firebase-admin');
// Initialize two app instances
const oldApp = adminOld.initializeApp(
oldServiceAccount,
'old-project'
);
const newApp = adminNew.initializeApp(
newServiceAccount,
'new-project'
);
// Determine which project to use based on token
async function sendMessage(token, message) {
// Try new project first (most tokens should be new)
try {
const messaging = newApp.messaging();
return await messaging.send({ token, ...message });
} catch (error) {
if (error.code === 'messaging/sender-id-mismatch') {
// Token belongs to old project
const messaging = oldApp.messaging();
return await messaging.send({ token, ...message });
}
throw error;
}
}4. Cleanup:
- Monitor token migration progress
- Remove old project configuration once all tokens migrated
- Update server to use only new project
### Understanding Sender ID Binding
Technical Details:
- Each FCM token contains an embedded signature tied to the sender ID (project number)
- The binding happens during token generation on the client device
- Firebase servers verify this signature on every message send
- This prevents token theft/reuse across different projects
Common Migration Scenarios:
1. Development to Production:
- Development app uses dev Firebase project
- Production app must use production Firebase project
- Tokens cannot be shared between these environments
2. Project Consolidation:
- Multiple apps moving to single Firebase project
- Each app needs fresh tokens from the consolidated project
- Old tokens from individual projects become invalid
3. Rebranding/Re-publishing:
- App package name changes require new Firebase project
- New package = new Firebase project = new tokens required
### Token Lifecycle Management
Best Practices:
1. Store project context with tokens: Record which Firebase project each token belongs to
2. Regular token refresh: Implement periodic token refresh (FCM does this automatically every ~6 months)
3. Validation before storage: Validate tokens match current project before storing in database
4. Cleanup invalid tokens: Remove tokens that fail with SENDER_ID_MISMATCH
Monitoring and Alerts:
- Track SENDER_ID_MISMATCH error rates
- Alert if error rate spikes (indicates configuration issue)
- Monitor token migration progress during project transitions
### Security Implications
The SENDER_ID_MISMATCH error is a security feature that:
- Prevents token reuse across projects
- Ensures messages only go to intended recipients
- Maintains project isolation in multi-tenant environments
Never attempt to "fix" this by modifying tokens or bypassing validation - instead, ensure proper project alignment.
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