I am developing the admin interface for my software and it was working fine in development (when I 'react start'). The problem is when I build and run it in production. React-admin won't load the data coming from the server, because of these 2 error in its requests.

OPTIONS http://localhost:3000/user?filter={}&range=[0,9]&sort=["id","ASC"] - CORS FAILED
GET http://localhost:3000/user?filter={}&range=[0,9]&sort=["id","ASC"] - NS_ERROR_DOM_BAD_URI

in development react-admin doesn't request 'options /user' neither I get these errors. I am using node express in the server side:

require('dotenv').config();
const express = require('express')
var cors = require('cors')
const app = express()
const port = process.env.SERVER_PORT;
const serverIp = process.env.SERVER_IP;
const { verifyUser } = require('./middleware/verification');
const { readUsers } = require('./db/dbManager');

app.use(cors())
app.get('/user', verifyAdmin, (req, res) => {
    readUsers().then((response) => {
        res.setHeader('Access-Control-Allow-Origin', '*');
        res.setHeader('Access-Control-Expose-Headers', 'Content-Range');
        res.setHeader('Content-Range', 'posts 0-24/319');
        res.setHeader('Content-Type', 'application/json');
        res.end(JSON.stringify(response));
    });
})

app.options('/user', verifyAdmin, (req, res) => {
    res.setHeader('Access-Control-Allow-Origin', '*');
    res.setHeader('Access-Control-Expose-Headers', 'Content-Range');
    res.setHeader('Content-Range', 'posts 0-24/319');
    res.setHeader('Content-Type', 'application/json');
    res.end();
})

app.use(express.static('build'));

app.listen(port, () => {
    console.log(`Example app listening at http://${serverIp}:${port}`)
});

How can I fix these errors I am having in production?