Traefik won't accept Bluemap and only give Gateway Timeouts or 404s

For context: Bluemap is a minecraft plugin that hosts a website alongside the minecraft instance which provides an interactive worldmap.

I host minecraft via docker-compose using itzg's docker image.
On the same machiene I host a traefik instance. Since the bluemap site is by default exposed without ssl on a custom port, I wanted to make it more secure by putting it behind my traefik instance.
Doing so was more complicated than I thought.

On Bluemap part, I changed the webroot directory config to represent the path inside the container to /data/bluemap/web in both web config files.
Also I changed the port of the webserver to 80.

On traefik part, I added my common labels and the web network to my docker-compose. But doing to would as I would soon lern only result in a Gateway Timeout.

Here are my compose files of minecraft and traefik:

I took one or two hours o trying to solve this issue but I am fully stuck...

The usual:

  1. Set to indicate which Docker network to use, which is shared between Traefik and target service

  2. Don’t use ports: on the target services to open ports on host. That enables to circumvent Traefik TLS and middlewares. Within the Docker network all ports are reachable.

  3. Use .loadbalancer.server.port= to indicate which internal target port to use per router/service.

  4. When multiple ports are used, you need multiple entrypoints, routers and services. Don’t forget to open the ports on Traefik container.

  5. Web GUI apps usually don’t like to be placed under a path prefix with PathPrefix(). Make sure the app is available internally on that changed path.