How to resolve the Socket.io error "ERR_NAME_NOT_RESOLVED - reactjs

Question

When I run my MERN Stack project on my localhost and get my app's render page, when I click on a button in my app, that button does and displays nothing. When I inspect my client-side render page, I see the following error:polling.js:311 GET http://%22http/socket.io/?EIO=4&transport=polling&t=O7Mtvxd net::ERR_NAME_NOT_RESOLVED. I don't know what it means, I searched the meaning on the internet but without success. Here is my backend index.js file:
const express = require('express')
const cors = require('cors')
const mongoose = require('mongoose')
require("dotenv").config()
const app = express()
const http = require('http')
const server = http.createServer(app)
const io = require('socket.io')(server)
const UserRoutes = require('./routes/User')
const AuthRoutes = require('./routes/Auth')
const PostRoutes = require('./routes/Post')
const PORT = process.env.PORT || 5000
const {MONGODB_URI} = require("./config")
app.use(cors())
app.use(express.json())
app.use((req, res, next) => {
io.req = req
req.io = io
next()
})
app.use('/api/auth', AuthRoutes)
app.use('/api/user', UserRoutes)
app.use('/api/post', PostRoutes)
require('./socket')(io)
mongoose
.connect(MONGODB_URI, {
useNewUrlParser: true,
useUnifiedTopology: true,
useCreateIndex: true,
})
.then(() => {
console.log('database connected')
server.listen(PORT, () => console.log(`server started on port ${PORT}`))
})
.catch((err) => console.log(err))
my backend socket.js file :
const User = require('./models/User')
const jwt = require('jsonwebtoken')
module.exports = (io) => {
io.on('connection', (socket) => {
if (io.req) {
socket.broadcast.emit('friend-login-status', { user_id: io.req.userId })
addSocketIdInDB(socket.id, io.req.userId)
socket.on('disconnect', () => {
socket.broadcast.emit('friend-logout-status', {
user_id: io.req.userId,
})
io.req.userId = null
})
}
})
}
async function addSocketIdInDB(socket_id, user_id) {
const user = await User.findById(user_id)
if (socket_id) {
user.socketId = socket_id
}
await user.save()
}
I looked on this question after this but without success. I work on Microsoft Edge .