Setting up a WebSocket connection over https?

Question

Node.js

Hello!
There is a client js:

let socket = io.connect('https://example.ru:3000');

There is server.js on the server:

var fs = require('fs');
let options = {
    key: fs.readFileSync('/etc/letsencrypt/live/example.ru/privkey.pem'),
    cert: fs.readFileSync('/etc/letsencrypt/live/example.ru/fullchain.pem'),
    port: 3000,
};
let https = require('https').createServer(options);
let io = require('socket.io')(https);
let Redis = require('ioredis');

let redis = new Redis();

redis.psubscribe('channel_*');
redis.on('pmessage', function (pattern, channel, message) {
    //console.log('Message recieved: ' + message);
    //console.log('Channel: ' + channel);
    msg = JSON.parse(message);
    io.emit(channel, msg);
});

https.listen(3000, function () {
    console.log('Listening on Port: 3000');
});

node server starts and runs, but then there is no connection in the browser.
Writes: WebSocket connection to 'wss://example.ru:3000/socket.io/?EIO=3&transport=websocket' failed: WebSocket is closed before the connection is established.
VPS: Apache, SSL per domain This is the
first time I've encountered such a task, can anyone tell me where to dig?
Thank you!