io.sockets.emit() won't work in production - node.js

Question

I am trying to setup a socket in production like so:
client :
import openSocket from 'socket.io-client';
function handleSomething() {
let socketServer = 'https://staging.app.xxx.eu:9999';
const socket = openSocket(socketServer);
socket.on('calendlyHook', () => {
console.log("*** HERE");
...
socket.emit('closeSocket');
socket.close();
socket.removeAllListeners();
});
}
server :
const app = require('express')();
const http = require('http').createServer(app);
const io = require('socket.io')(http);
function openSocket() {
io.close();
io.set('origins', '*:*');
io.on('connection', (client) => {
console.log('Socket connected');
client.on('closeSocket', () => {
io.close();
io.removeAllListeners();
console.log('Socket closed');
});
});
const port = 9999;
io.listen(port);
console.log('*** listening on port ', port);
}
Then server-side, another function tries the following:
io.emit('calendlyHook');
or
io.sockets.emit('calendlyHook');
I have several issues in production (none of which happen on localhost):
console.log('*** listening on port ', port) is working fine
console.log('Socket connected') is not happening
io.emit('calendlyHook') or io.sockets.emit('calendlyHook') are not doing anything
I do not have any web server proxy set up on that url.
What is wrong here? Thanks!