WebSocket error on wordpress simply chat. How to fix?

Question

Node.js

Hello! Can you help me figure out why the chat on the site is not working?
I am using this plugin https://codecanyon.net/item/simplychat-for-buddypr...
The developer says everything should work but it doesn't.
Throws this error:
WebSocket connection to 'wss://sunline.kiev.ua/socket.io/?uid=6&away=null&EIO=3&transport=websocket' failed: Error during WebSocket handshake: Unexpected response code: 404 Worked
without SSL, but when I installed the certificate, it does not work. I thought that it did not work because of a self-signed certificate, but I put a normal certificate and still there is no result.