Deploy React with Heroku - node.js

Question

Hi i'm trying to deploy my project with heroku but it's impossible i don't understand
I already did like that on other project but this time it doesn't works in my server.js i have this code :
const express = require("express");
const graphqlHTTP = require("express-graphql");
const cors = require("cors");
const schema = require("./schema");
const path = require("path");
const app = express();
//allow Cross origin
app.use(cors());
app.use(
"/graphql",
graphqlHTTP({
schema,
graphiql: true
})
);
app.use(express.static('public'));
app.get("*", (req, res) => {
res.sendFile(path.resolve(__dirname, 'public', 'index.html'));
});
const PORT = process.env.PORT || 5000;
app.listen(PORT, () => console.log(`Server started on port ${PORT}`));
In my app.js who is in my Client folder i modify uri for AplolloClient :
import React from 'react';
import './App.css';
import Logo from "./logo.png";
import Matchs from './components/Matchs'
import MatchDetail from './components/MatchDetail'
import ApolloClient from "apollo-boost";
import { ApolloProvider } from "#apollo/react-hooks";
import { BrowserRouter as Router, Route } from "react-router-dom";
const client = new ApolloClient({
uri: "/graphql"
});
function App() {
return (
<ApolloProvider client={client}>
<Router>
<div className="container">
<img
src={Logo}
alt="Nba App"
style={{ width: 300, display: "block", margin: "auto" }}
/>
<Route exact path="/" component={Matchs} />
<Route exact path="/match/:gameId" component={MatchDetail} />
</div>
</Router>
</ApolloProvider>
);
}
export default App;
in my package.json from my client folder i add a proxy :
{
"name": "client",
"version": "0.1.0",
"private": true,
"dependencies": {
"#apollo/react-hooks": "^3.1.3",
"#testing-library/jest-dom": "^4.2.4",
"#testing-library/react": "^9.3.2",
"#testing-library/user-event": "^7.1.2",
"apexcharts": "^3.15.5",
"apollo-boost": "^0.4.7",
"classnames": "^2.2.6",
"graphql": "^14.6.0",
"lodash.flowright": "^3.5.0",
"react": "^16.12.0",
"react-apexcharts": "^1.3.6",
"react-apollo": "^3.1.3",
"react-dom": "^16.12.0",
"react-icons": "^3.9.0",
"react-router-dom": "^5.1.2",
"react-scripts": "3.3.1"
},
"scripts": {
"start": "react-scripts start",
"build": "react-scripts build && mv build ../public",
"test": "react-scripts test",
"eject": "react-scripts eject"
},
"eslintConfig": {
"extends": "react-app"
},
"browserslist": {
"production": [
">0.2%",
"not dead",
"not op_mini all"
],
"development": [
"last 1 chrome version",
"last 1 firefox version",
"last 1 safari version"
]
},
"proxy": "http://localhost:5000"
}
And i made a script to build and move in public/build
But when i deploy in heroku i have always
VM165:1 POST http://localhost:4000/graphql net::ERR_CONNECTION_REFUSED
But i don't know where he take this Url because i think i change all places where it could be problematic
Thanks a lot