MERN File upload

react_client.js

// client 

import React, {useState} from 'react'
import axios from 'axios'

export default function Image() {

    const [Image, setImage] = useState('Choose File');
    const [ImageUrl, setImageUrl] = useState('Choose File');
    
    const handleSubmit = (e) => {
      e.preventDefault();
      const formData = new FormData();
      formData.append('avatar', Image);
      
      axios.post(`/upload`,formData)
        .then(res =>{
            console.log(res)
            setImageUrl(res.data.url)
        })
        .catch(err => {
            console.log(err)
        })
    };
    return (
        <form onSubmit={handleSubmit}>
          <input type="file" name="image" onChange={e=>setImage(e.target.files[0] )} required />
          <button type="submit">Add</button>
        </form>
    )
}

server.js

// server

const express = require('express');
const mongoose = require('mongoose');
require('dotenv').config()
var cors = require('cors')
const cloudinary = require("cloudinary").v2;
var multer  = require('multer')
var upload = multer({ dest: 'uploads/' })


// mongodb setup
const dbURI = process.env.DB_URL;
mongoose.connect(dbURI, { useNewUrlParser: true, useUnifiedTopology: true })
  .then(result => console.log('connected to db'))
  .catch(err => console.log(err));

const app= express();
app.use(express.json())
app.use(cors())

cloudinary.config({
  cloud_name: process.env.CLOUDINARY_CLOUD_NAME,
  api_key: process.env.CLOUDINARY_API_KEY,
  api_secret: process.env.CLOUDINARY_API_SECRET
});


app.post('/profile',upload.single('avatar'),(req,res)=>{
  console.log(req.file)
  cloudinary.uploader.upload(req.file.path)
      .then((result) => {
      console.log(result)
      res.status(200).send({
          uploaded: "true",
          url : result.url
      });
      })
      .catch((error) => {
      console.log(error)
      res.status(404).send({error});
      });
})

const port = process.env.PORT || 5000
app.listen(port, console.log(`app is running on port ${port}, go to http://localhost:${port}`))

I think you forgot to add this.

axios.defaults.baseURL = http://localhost:5000