projeto-hit/frontend/src/services/socket.js

import { io } from 'socket.io-client';

// "undefined" means the URL will be computed from the `window.location` object
const URL = process.env.REACT_APP_BACKEND_URL

export const socket = io(URL, 
//{
//     withCredentials: true,
//     extraHeaders: {
//         "my-custom-header": "abcd"
//     },
    // transports: ['websocket',  'polling']
//}
);