Reactjs – error , backend not running on port 4000 (used )

im not using port 4000 it said im using it i tried to kill any process using 4000 port i didnt find any here the error msg : enter image description here

i tried to run the backend project and here’s the index.js code :

const express = require('express');
const sql = require('mssql');
const cors = require('cors');
const app = express();
const port = 4000;

// SQL Server configuration
const config = {
    user: 'machine datas',
    password: 'das',
    server: 'MSI',
    database: 'Mach',
    dialect: "mssql",
    options: {
        encrypt: true,
        trustServerCertificate: true ,  // Change to true for self-signed certificates
        trustedConnection : false ,
        enableArithAbort : true ,
        instancename : 'SQL EXPRESS' ,


    }

};

// Connect to SQL Server



sql.connect(config)
    .then(pool => {
        if (pool.connecting) {
            console.log('Connecting to SQL Server...');
        } else {
            console.log('Connected to SQL Server!');
        }
    })
    .catch(err => {
        console.error('SQL Server connection error:', err);
    });

// Route for the root path
app.get('/', (req, res) => {
    res.send('Welcome to the API!');
});
//  route
app.get('/data', async (req, res) => {
    try {
        const result = await sql.query('SELECT * FROM aaxeee');
        console.log('Data fetched from SQL Server:', result.recordset);
        res.json(result.recordset);
    } catch (err) {
        console.error('SQL query error:', err);
        res.status(500).send('Server error');
    }
});

app.listen(port, () => {
    console.log(`Server is running on http://localhost:${port}`);
});




app.use(cors()); // This will allow all origins by default





app.get('/api/items', (req, res) => {
    res.json([{ /*  */ }]);



});



app.listen(4000, () => console.log('Server running on port 4000'));
 

i didn’t understand fully what is happening even tough i changed the port multiple times and killed any process used by any port i tried to enter i don’t know if it could be the configuration or something else its my first time creating a backend project .