admin.messaging() is not a function while on "firebase-admin": "^11.3.0",

I’ve been trying to send a notfication to topic "All" and the console log shows error:

Notification sent failed: TypeError: admin.messaging is not a function

Code:

// The Cloud Functions for Firebase SDK to create Cloud Functions and set up triggers.
const functions = require('firebase-functions');

// The Firebase Admin SDK to access Firestore.
var admin = require("firebase-admin/app");
const { applicationDefault } = require('firebase-admin/app');

admin.initializeApp({
  credential: applicationDefault(),
  databaseURL: "my-firebase-url"
});

exports.notificationsOnCreate = functions.database.ref("/{type}/{id}/").onCreate(async (snapshot, context) => {
  const payload = {
    notification: {
      title: 'cloud function demo',
      body: 'this is a test notification'
    }
  };
  
  try{
    return await admin.messaging().sendToTopic("All", payload)
    .then(function(response){
    console.log('Notification sent successfully: ', response);
    });
  } catch(err) {
    console.log('Notification sent failed: ', (err));
  }
})

Other stack overflow topics recommend updating firebase-admin to a version >5.1, but that seems to not be the issue here.

package.json file:

{
  "name": "functions",
  "description": "Cloud Functions for Firebase",
  "scripts": {
    "serve": "firebase emulators:start --only functions",
    "shell": "firebase functions:shell",
    "start": "npm run shell",
    "deploy": "firebase deploy --only functions",
    "logs": "firebase functions:log"
  },
  "engines": {
    "node": "16"
  },
  "main": "index.js",
  "dependencies": {
    "firebase-admin": "^11.3.0",
    "firebase-functions": "^4.1.0"
  },
  "devDependencies": {
    "firebase-functions-test": "^0.2.0"
  },
  "private": true
}

>Solution :

import from firebase-admin instead of firebase-admin/app

// The Firebase Admin SDK to access Firestore.
var admin = require("firebase-admin");