Digitaclocean blockeing socket.io

In my localhost socket.io working correctly, but in droplet it’s not working because socket.io requesting to http from https. How much I understand I can not add ssl certificate for ip address. The solution is instead ip address use domain, but in this case I don’t know how to create open port for domain not for ip address.

server.js

const options = {
    cors: {
        origin: "https://example.com",
        methods: ["GET", "POST"]
    },
    transports: ['websocket', 'polling'],
};

const http = require('http').Server();
const io = require('socket.io')(http, options);

io.on('connection', function (socket) {
    socket.on('message', function (data) {
        io.sockets.emit('add-review', data);
    })
});

http.listen(6001, '0.0.0.0', function(){
    console.log('listening on *:6001');
});

client.js

var socket = io('https://ip-address:6001');