Mongodb – I have Created a Whatsapp Clone using MERN Stack. Facing Errors in backEnd side

I have created a WhatsApp clone in the backend of Whatsapp clone i am facing following errors.
when i run yarn start i am facing following errors in console.

        yarn start
yarn run v1.23.0-20200615.1913



  $ node server.js
(node:4316) [MONGODB DRIVER] Warning: the options [useUnifedTopology] is not supported
(Use `node --trace-warnings ...` to show where the warning was created)
listen on local host 6000

(node:4316) [MONGODB DRIVER] Warning: Current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.

E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoretopologiesserver.js:441
          new MongoNetworkError(
          ^

MongoNetworkError: failed to connect to server [cluster0-shard-00-01.ngclm.mongodb.net:27017] on first connect [MongoError: bad auth : Authentication failed.
    at Connection.messageHandler (E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionconnection.js:362:19)
    at Connection.emit (node:events:390:28)
    at processMessage (E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionconnection.js:454:10)
    at TLSSocket.<anonymous> (E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionconnection.js:623:15)
    at TLSSocket.emit (node:events:390:28)
    at addChunk (node:internal/streams/readable:315:12)
    at readableAddChunk (node:internal/streams/readable:289:9)
    at TLSSocket.Readable.push (node:internal/streams/readable:228:10)
    at TLSWrap.onStreamRead (node:internal/stream_base_commons:199:23) {
  ok: 0,
  code: 8000,
  codeName: 'AtlasError'
}]
    at Pool.<anonymous> (E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoretopologiesserver.js:441:11)
    at Pool.emit (node:events:390:28)
    at E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionpool.js:564:14
    at E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionpool.js:1013:9
    at callback (E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionconnect.js:75:5)
    at E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionconnect.js:147:27
    at E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreauthscram.js:109:14
    at _callback (E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionconnection.js:331:7)
    at Connection.messageHandler (E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionconnection.js:362:9)
    at Connection.emit (node:events:390:28)
    at processMessage (E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionconnection.js:454:10)
    at TLSSocket.<anonymous> (E:Whatapp clonewhatsapp-backendnode_modulesmongodblibcoreconnectionconnection.js:623:15)
    at TLSSocket.emit (node:events:390:28)
    at addChunk (node:internal/streams/readable:315:12)
    at readableAddChunk (node:internal/streams/readable:289:9)
    at TLSSocket.Readable.push (node:internal/streams/readable:228:10)

My main file Server.js (It is the main file )

// Import

import express from "express";
import mongoose from "mongoose";
import Messages from './dbMessages.js';
import Pusher from "pusher";
import cors from "cors";

import axios from "axios";

// app config
const app = express();
const port = process.env.PORT || 6000;

// Pusher code
const pusher = new Pusher({
    appId: "1366318",
    key: "eb9c7412499f6e7b4c5f",
    secret: "6903a1ffa86fcb2c3ddd",
    cluster: "ap2",
    useTLS: true
  });
  
// middle ware
app.use(express.json());
app.use(cors());
app.use((req,res, next ) => {
    res.setHeader("Access-Control-Allow-Origin" ,"*");
    res.setHeader( "Access-Control-Allow-Origin" ,"*");
    next();
});
// DB Config
const connection_url='mongodb+srv://whatsapp:[email protected]/whatsapp?retryWrites=true&w=majority';

mongoose.connect(connection_url,{
    useCreateIndex: true,
    useNewUrlParser: true,
    useUnifedTopology: true
})

// ?????
const db = mongoose.connection;

db.once("open",()=>{
    console.log("db connected");
    // message contents is from mongodb database
    const msgCollection = msgCollection('whatsapp'); //collection name in mongodb messagecontents
    // messagecontents changing to whatsapp
    const changeStream = msgCollection.watch();
    // Change Stream  function
    changeStream.on("change", (change) => 
    {
        // this is when we troggling pusher
        console.log('A changed is occur',change);

        if (change.operationType === 'insert'){
            const messageDetails = change.fullDocument;
            pusher.trigger('message', 'insert', {
                name:messageDetails.user,
                message: messageDetails.message,
                timeStamp: messageDetails.timeStamp,
                received: messageDetails.received
            });
        } else {
            console.log('Error Troggling pusher');
        }
    });
});
// api router
app.get('/',(req,res) => {
    res.status(200).send("Hello World");
});

// api to get all the data from database
app.get('/messages/sync' , (req,res) => {
//    Messsages.find() to get back all the messages
   Messages.find((err,data) => {
        if (err) {
            res.status(500).send(err)
        }
         else {
             res.status(200).send(data)
         }
    });
});


app.post('/api/messages/new', (res,req) => {
    const dbMessage = req.body 
    message.create(dbMessage, (err,data)=>{
        if (err){
            res.status(500).send(err)
        }
        else {
            res.status(201).send(`new number created: n ${data}`)
        }

    });
});
// listen
app.listen(port, () => console.log(`listen on local host ${port}`));

MY schema (dbMessages.js)

import mongoose from "mongoose";

const whatsappSchema = mongoose.Schema({
    message:String,
    name:String,
    timestamp:String
});

export default mongoose.model('whatsapp', whatsappSchema);

My Package.Json

{
  "name": "whatsapp-backend",
  "version": "1.0.0",
  "discription": "",
  "main": "server.js",
  "type": "module",
  "scripts": {
    "test": "echo "Error: no test specified" && exit 1",
    "start": "node server.js",
    "nodemon":"nodemon --experimental-modules --es-module-specifier-resolution=node "
  },
  "keywords": [],
  "author": "zain",
  "license": "ISC",
  "dependencies": {
    "cors": "^2.8.5",
    "express": "^4.17.3",
    "express_js": "^1.0.0",
    "mongoose": "^6.2.5",
    "nodemon": "^2.0.15",
    "pusher": "^5.0.1",
    "pusher-js": "^7.0.6"
  }
}