Provisional headers are shown socket io - express

Question

I am trying to set up socket io for the first time in a production env. I think I am running into some CORS related issues.
Currently the error I am getting is
Provisional headers are shown
Server side code:
app.js
app.io.attach(server);
index.js
app.io = require('socket.io')({origins: allowed_header});
On client side:
const socket = io(process.env.SOCKET_ADDRESS);
where socket address is http://localhost:8080 for dev, and https://websiteName.com:8080 for production
The server uses nginx's default port. The app works fine when running locally, but it logs in above error in production env.
Thanks
UPDATE:
I tried to change my local client to connect to remote server. And it works this way as well. It is just my production client now have the following issue:
Failed to load resource: the server responded with a status of 403 (Forbidden)
UPDATE2:
I could not really solve the problem, so instead I just did the following:
origins: ['http://localhost:3000', 'http://localhost:4000', '*:*']
And it works for now, but I'd like to figure out what is going on. I tried to replace : with https://example.com:80, and this didn't work.

Answer 1

Hope this will help with all the CORS error
const cors = require('cors');
app.use(cors());
Docs CORS