MongoDB connection error: MongoTimeoutError: Server selection timed out after 30000 ms

I am trying to create a fullstack app reading the following tutorial:

https://medium.com/javascript-in-plain-english/full-stack-mongodb-react-node-js-express-js-in-one-simple-app-6cc8ed6de274

I followed all steps and then tried to run:

node server.js

But I got the following error:

MongoDB connection error: MongoTimeoutError: Server selection timed
out after 30000 ms
at Timeout._onTimeout (C:\RND\fullstack_app\backend\node_modules\mongodb\lib\core\sdam\server_selection.js:308:9)
at listOnTimeout (internal/timers.js:531:17)
at processTimers (internal/timers.js:475:7) { name: ‘MongoTimeoutError’, reason: Error: connect ETIMEDOUT
99.80.11.208:27017
at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1128:14) {
name: ‘MongoNetworkError’,
[Symbol(mongoErrorContextSymbol)]: {} }, [Symbol(mongoErrorContextSymbol)]: {} } (node:42892)
UnhandledPromiseRejectionWarning: MongoTimeoutError: Server selection
timed out after 30000 ms
at Timeout._onTimeout (C:\RND\fullstack_app\backend\node_modules\mongodb\lib\core\sdam\server_selection.js:308:9)
at listOnTimeout (internal/timers.js:531:17)
at processTimers (internal/timers.js:475:7)

My code at server.js is as follows:

const mongoose = require('mongoose');
const router = express.Router();

// this is our MongoDB database
const dbRoute =
    'mongodb+srv://user:<password>@cluster0-3zrv8.mongodb.net/test?retryWrites=true&w=majority';

mongoose.Promise = global.Promise;

// connects our back end code with the database
mongoose.connect(dbRoute, 
    {   useNewUrlParser: true,
        useUnifiedTopology: true
    });

let db = mongoose.connection;

db.once('open', () => console.log('connected to the database'));

Any suggestions?