Guide

Common FCM HTTP v1 Errors and Fixes

Troubleshoot 401, 403, 404, and invalid-argument errors when sending Firebase Cloud Messaging notifications.

Last updated: May 2026

Developer reviewing source code to fix FCM HTTP v1 API errors — Check token expiry, Project ID, and string-only data payload values

401 UNAUTHENTICATED

The OAuth access token is missing, expired, or invalid. Generate a new token with gcloud auth print-access-token. Confirm you are not using the device token in the Authorization header.

Code editor on screen while debugging a failed FCM API response — 401 errors almost always mean an expired or wrong OAuth access token

403 PERMISSION_DENIED

The authenticated identity lacks cloudmessaging.messages.create on the project. Add Firebase Cloud Messaging Admin role in IAM, or use an account with Owner/Editor on the Firebase project.

404 NOT_FOUND (invalid token or project)

The device token may be unregistered or belong to a different Firebase project. The Project ID in the URL must match the project that issued the token. Uninstall and reinstall the app to get a new token.

400 INVALID_ARGUMENT

Data payload values must be strings, not numbers or objects
Malformed JSON in custom data fields
Empty or truncated device token
Invalid image URL in notification payload

Notification not visible on device

If the app is in foreground, notification messages may not show a system banner unless you handle them in code. Data-only messages never show a tray notification by default. Check battery optimization and notification channel settings on Android.

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