How to connect react js frontend with express api backend

I am trying to create a axios post request to my express backend from my react front end

i have tried including the proxy syntax to my package json so it can interact to it and i have also tried React Proxy error: Could not proxy request /api/ from localhost:3000 to http://localhost:8000 (ECONNREFUSED)

Here is my client package.json

  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },

  "proxy": "http://localhost:5000",

And here is my api request

axios
      .post('api/users/register', newUser)
      .then(res => console.log(res.data))
      .catch(err => this.setState({ errors: err.response.data }));

here is my express back end, Note i have a api folder that handles each api

const express = require('express');
const mongoose = require('mongoose');
const bodyParser = require('body-parser');
const passport = require('passport');

const users = require('./routes/api/users');
const posts = require('./routes/api/posts');
const movies = require('./routes/api/movies');

const app = express();

// Body parser middleware
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());

// Connect to MongoDB
mongoose
  .connect("<my mongo db>", { useNewUrlParser: true })
  .then(() => console.log('MongoDB Connected'))
  .catch(err => console.log(err));

// Passport middleware
app.use(passport.initialize());

// Passport Config
require('./config/passport')(passport);

// Use Routes
app.use('/api/users', users);
app.use('/api/posts', posts);
app.use('/api/movies', movies);

const port = process.env.PORT || 5000;

app.listen(port, () => console.log(`Server running on port ${port}`));

But my react app is running on port 3000

I expect it to output a success message in console, but here is what i got

POST http://localhost:3000/api/users/register 404 (Not Found) xhr.js:166

which shows it is not communicating with my package json proxy.