EADDRINUSE error when creating an express server with next.js

Question

I'm working on a project with next.js and I'm trying to set up an express server but getting the following error:

This is the server.js:

const express = require('express');
const next = require('next');

const dev = process.env.NODE_ENV !== 'production';
const app = next({dev});
const handle = app.getRequestHandler();

app.prepare()
.then(() => {
     const server = express();

     server.get('*', (req, res) => {
          return handle(req, res);
     });

     server.listen(3000, (err) => {
          if (err) throw err;
          console.log('> Ready on http://localhost:3000');
     });
})
.catch((ex) => {
     console.error(ex.stack);
     process.exit(1);
});

and the package.json:

{
  "name": "makeyka",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "dev": "node server.js",
    "build": "next build",
    "start": "NODE_ENV=production node server.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "@zeit/next-sass": "^1.0.1",
    "axios": "^0.19.0",
    "express": "^4.17.1",
    "next": "^9.0.6",
    "node-sass": "^4.12.0",
    "react": "^16.9.0",
    "react-dom": "^16.9.0"
  }
}

As I'm new to next and express I can't figure out the problem here