nginx logging (111: connection refused) when connecting to a websocket

Question

So I have a small Raspberry Pi on my local network that I use to host a server. It is a fairly simple setup, with nginx and my npm-hosted server stood up in containers using docker-compose.

my npm server listens to port 30000.

Here is my nginx setup

   server {
        # Listen on port 80
        listen 80;
        listen [::]:80;
    
        # Sets the Max Upload size to 100 MB
        client_max_body_size 100M;

        # Enable compression
        gzip on;
        gzip_disable "MSIE [1-6]\.";

        gzip_comp_level 6;
        gzip_min_length 1024;
        gzip_buffers 16 8k;
        gzip_proxied any;
        gzip_types
            <a bunch of gzip types>

        # Proxy Requests to server
        location / {
    
            # Set proxy headers
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;
    
            # These are important to support WebSockets
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "Upgrade";
    
            # Make sure to set your port number
            proxy_pass http://npmServer:30000;
        }
    }

When I am serving static content I have no problem. But when I am trying to connect to ws://<PiIP>/socket.io/... I get a connection failed message in my browser terminal, and when I check my logs in docker compose, I see a bunch of connect() failed (111: Connection Refused) errors.

Is there a way to add a socket.io location somehow? I have even spoken to some folks who are hosting the same npm-based project using the exact same setup, and they also have no idea what is going on.