React/Socket.io client not connecting to server when deployed to Heroku - node.js

Question

I'm following this tutorial: https://www.youtube.com/watch?v=tBr-PybP_9c
Locally, the app works fine - I can open up some windows and have them talk to each other. However, when I try to deploy the app to Heroku, the clients no longer connect to the server.
Server-side:
const express = require('express');
const cors = require('cors');
const socket = require('socket.io');
const dotenv = require('dotenv');
dotenv.config({ path: './config.env' });
const app = express();
app.use(cors());
const port = process.env.PORT || 8080;
const server = app.listen(port, () => {
console.log(`App running on port ${port}`);
});
const http = require('http').Server(app);
const io = socket(http, {
pingInterval: 100,
pingTimeout: 500,
cors: {
origin: '*',
},
});
io.listen(server);
io.on('connection', (socket) => {
const id = socket.handshake.query.id;
socket.join(id);
console.log(`A user has connected with ID ${id}`);
});
I deployed the server to a Heroku dyne, and it built successfully. The client is a separate dyne:
import React, { useContext, useEffect, useState } from 'react';
import io from 'socket.io-client';
const SocketContext = React.createContext();
export function useSocket() {
return useContext(SocketContext);
}
export function SocketProvider({ id, children }) {
const [socket, setSocket] = useState();
useEffect(() => {
// const newSocket = io('https://my-heroku-app.herokuapp.com:48600', {
const newSocket = io('http://localhost:8080', {
query: { id },
});
setSocket(newSocket);
return () => newSocket.close();
}, [id]);
return (
<SocketContext.Provider value={socket}>{children}</SocketContext.Provider>
);
}
This also built successfully. Obviously, localhost:8080 doesn't work when deployed to Heroku - I tried using 'https://my-heroku-app.herokuapp.com:48600' (the server application's name plus the port where it's running on Heroku), and that doesn't work either. The console.log never occurs on the server side when I do heroku logs --tail.
Is there a better way to do this? Can I put these into the same app, so I only have to deploy one project?