How to fix messaging/mismatched-sender-id in Firebase

import { initializeApp } from "firebase/app";
import { getMessaging, getToken } from "firebase/messaging";

const firebaseConfig = {
  apiKey: "YOUR_API_KEY",
  projectId: "YOUR_PROJECT_ID",  // This must match your server project
  messagingSenderId: "YOUR_SENDER_ID",  // Verify this matches Firebase Console
  appId: "YOUR_APP_ID",
};

const app = initializeApp(firebaseConfig);
const messaging = getMessaging(app);

getToken(messaging, {
  vapidKey: "YOUR_VAPID_KEY"
}).then(token => {
  console.log("Registration token:", token);
});

<!-- Check your google-services.json file contains the correct project ID -->
<!-- The Sender ID in google-services.json must match your Firebase project -->

const admin = require("firebase-admin");
const serviceAccount = require("./serviceAccountKey.json");

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
  // Note: Do NOT override the project ID. Admin SDK uses the project ID
  // from your service account JSON file. This MUST match your client project.
});

// Verify the project ID
console.log("Server using project:", admin.app().options.projectId);

// Send a message
admin.messaging().sendToDevice(registrationToken, message)
  .catch(error => {
    if (error.code === "messaging/mismatched-sender-id") {
      console.log("Client and server using different Firebase projects!");
    }
  });

import { getMessaging, getToken, deleteToken } from "firebase/messaging";

const messaging = getMessaging();

// Delete old token (optional, forces new token generation)
await deleteToken(messaging);

// Request new token with fresh configuration
const token = await getToken(messaging, {
  vapidKey: "YOUR_VAPID_KEY"
});

console.log("New registration token:", token);

// Send this new token to your server to replace the old one
await fetch("/api/update-token", {
  method: "POST",
  body: JSON.stringify({ token })
});

import com.google.firebase.messaging.FirebaseMessaging;

// Firebase automatically generates a new token when re-initialized
// with correct google-services.json
FirebaseMessaging.getInstance().getToken()
  .addOnCompleteListener(task -> {
    if (!task.isSuccessful()) {
      Log.w(TAG, "Fetching FCM registration token failed", task.getException());
      return;
    }
    String token = task.getResult();
    Log.d(TAG, "New FCM Token: " + token);
  });

const admin = require("firebase-admin");

const message = {
  notification: {
    title: "Test Notification",
    body: "If you see this, sender ID is now matched!"
  },
  token: newRegistrationToken  // Use the newly generated token
};

admin.messaging().send(message)
  .then(response => {
    console.log("Message sent successfully:", response);
  })
  .catch(error => {
    if (error.code === "messaging/mismatched-sender-id") {
      console.log("Still mismatched! Check configuration again.");
    } else {
      console.log("Error sending message:", error);
    }
  });