WebSocket use in App Platform (wss)

I have a react frontend and a .NET Core 8.0 backend that works beautifully on dev machine.

Finally decided to deploy it via App Platform but I’m having issues with secure websocket communication.

As I understand it, AP is handling my SSL stuff so I just need to properly specify the URLs in my environment variables.

My working dev variables look like this:

REACT_APP_API_URL=http://localhost:5000/api
REACT_APP_WS_URL_ws=ws://localhost:5000/ws
REACT_APP_WS_URL_game=ws://localhost:5000/game

So I made my .env.production variables as such:

REACT_APP_API_URL=https://mydomain.com/api
REACT_APP_WS_URL_ws=wss://mydomain.com/ws
REACT_APP_WS_URL_game=wss://mydomain.com/game

While the API calls work fine, the WebSocket connection fails with the following error:

Firefox can't establish a connection to the server at wss://mydomain.com/ws

Testing the WebSocket connection directly via Postman connects successfully.

I use an Nginx configuration that I copy into my Dockerfile for the frontend. Here’s the Nginx configuration:

nginx
server {
    listen 80;
    server_name mydomain.com;

    location / {
        root /usr/share/nginx/html;
        try_files $uri $uri/ /index.html;
    }

    location /api/ {
        proxy_pass http://backend-api:5000;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }

    location /ws/ {
        proxy_pass http://backend-api:5000/ws;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";  # Corrected case
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_cache_bypass $http_upgrade;
    }

    location /game/ {
        proxy_pass http://backend-api:5000/game;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";  # Corrected case
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_cache_bypass $http_upgrade;
    }
}

In this configuration, “backend-api” is the name of my backend compute section.

I’m seeking advice on what else could be causing this issue or if there are any additional configurations I need to make for WebSocket connections to work correctly in production on DigitalOcean App Platform.