FCM: send()/sendEachForMulticast() with fid return NotRegistered for a FID that Console delivers to at the same moment #3288

[READ] Step 1: Are you in the right place?

Yes — this is about the code in firebase-admin-node itself (Messaging.send() / Messaging.sendEachForMulticast() FID targeting).

[REQUIRED] Step 2: Describe your environment

• Operating System version: Ubuntu 24.04.4 LTS (WSL2, kernel 6.6.114.1-microsoft-standard-WSL2)
• Firebase SDK version: firebase-admin 14.5.0 (also reproduces on ^14.4.0); client-side firebase 12.19.0 / @firebase/messaging 0.13.3
• Firebase Product: Cloud Messaging (FCM) — Firebase Installation ID (FID) targeting
• Node.js version: 22.23.x
• NPM version: 10.8.2 (package management via pnpm workspaces; npm version given for reference)

[REQUIRED] Step 3: Describe the problem

Steps to reproduce:

1. Client registers for push notifications using the new FID-based API: register(messaging, { vapidKey, serviceWorkerRegistration }) from firebase/messaging.
   onRegistered fires with FID ceewOt8IieuDcWg1YUkduN.
2. In the Firebase Console → Cloud Messaging → Compose notification → Send test message, the same FID is pasted into "Firebase Installation ID or FCM registration
   token". Delivery succeeds.
3. From a Node backend using firebase-admin, both of the following are called for the same FID and both fail:

   await getMessaging().send({
     fid: 'ceewOt8IieuDcWg1YUkduN',
     notification: { title, body },
   });
   // and
   await getMessaging().sendEachForMulticast({
     fids: ['ceewOt8IieuDcWg1YUkduN'],
     notification: { title, body },
   });

   Both reject / return success: false with a NotRegistered error (see Relevant Code for the full error object).
4. Immediately after step 3's failure (within the same minute), repeating step 2 (Console test send) with the identical FID succeeds again.

This rules out:

• Propagation delay (Console succeeds within the same minute as the failed Admin SDK calls, both before and after).
• A multicast-specific bug (reproduces identically on both send() and sendEachForMulticast()).
• Project/config mismatch (firebase use confirms the same project, refpro-app-staging, as the client's VITE_FIREBASE_PROJECT_ID).

Note: this reproduction was observed while running the backend via the Firebase Functions emulator (firebase emulators:start --only functions), authenticated
via a firebase login user session (no GOOGLE_APPLICATION_CREDENTIALS / gcloud ADC configured locally) rather than a deployed function's service account.
Re-testing against a real deployed Cloud Function (with its actual runtime service account) is still pending on our side — flagging this in case the discrepancy turns
out to be credential-identity-related rather than an SDK bug; will update this issue once confirmed either way.

Possibly related: #2970 reports Console succeeding while Admin SDK's sendEachForMulticast() fails with a 404, but with a different error shape (raw HTML, not a
structured NotRegistered error) and using legacy tokens rather than FIDs — closed by the reporter without explanation, so inconclusive whether it's the same root
cause.

Relevant Code:

import { getMessaging } from 'firebase-admin/messaging';

const response = await getMessaging().sendEachForMulticast({
  fids: ['ceewOt8IieuDcWg1YUkduN'],
  notification: { title: 'Test', body: 'Test' },
});
// response.responses[0] => { success: false, error: FirebaseMessagingError }

FirebaseMessagingError: NotRegistered
  code: 'messaging/installation-id-not-registered',
  cause: RequestResponseError: Server responded with status 404.
  httpResponse: { status: 404, ... }
  codePrefix: 'messaging'