Internal server error while routing to different page in production

[sujoys10]

I have built a realtime app in nextJS with socket.io. I am using custom server to setup web socket.
It is working perfectly fine in local machine.
But In production, I am getting internal server error while routing to different page from home page.

eg: https://movie-cricket.herokuapp.com/home

Server.js

const app = require('express')();
const server = require('http').createServer(app);
const io = require('socket.io')(server);
const next = require('next');
const dev = process.env.NODE_ENV !== 'production';
const nextApp = next({ dev });
const handler = nextApp.getRequestHandler();

nextApp.prepare().then(() => {

    app.get('/online', (req, res) => {
        const online = count;
        res.json(online);
    })
    
    app.get('/roomlist', (req, res) => {
        const roomlist = rooms.getRoomList();
        res.json(roomlist);
    })

    app.get('*', (req, res) => {
        return handler(req, res)
    })

    server.listen(port, err => {
        if(err) throw err;
        console.log(`server is running on port: ${port}`)
    })
})

Here is the github repo for reference. github