Docker Mattermost / NGINX Websocket Error 400

I have a docker mattermost running and it works perfectly when opened directly through server IP and Docker mapped port (192.168.0.5:33000) Everything works great.

The problem is when I try to make it work through NGINX proxy. The website itself works, I can login and go into channels and everything, but when typing a message I get:

WebSocket connection to 'wss://chat.spntt.com/api/v3/users/websocket' failed: Error during WebSocket handshake: Unexpected response code: 400, and I get the "Please check connection, Mattermost unreachable, if issue persists, ask administrator to check WebSocket port."

And this repeats for every message typed in chat. I tried adding additional nginx rules as below but is still does not work.

location /api/v3/ {
proxy_pass http://192.168.0.5:33000;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_set_header Host $host;
}