How do I activate reverse proxy with swag & docker-compose

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server

HTTP

docker

The following three containers are managed in docker-compose. 'docker-compose up' solves all 3 containers with no errors, and my application works properly when 'docker swag flag -f' is called. I followed these instructions to set up and edit the conf files.
https://docs.linuxserver.io/general/swag#subdomain-proxy-conf[^]
reverse-proxy-confs/README.md at master · linuxserver/reverse-proxy-confs · GitHub[^]

I have 2 problems:

If I understand correctly, it should now be possible to access the url 'plex.fermentedbeans.coffee' from a browser, but it doesn't, so what am I forgetting / misunderstanding?? (Without the subdomain plex, the url works.)

Secondly, calling docker swag flag from command line of the remote server starts the application, but calling the url from the browser gives the html page. Where can I change this to starting the app?
Regarding this, I am assuming I need to change the line

index index.html index.htm index.php;

in the main server block of the sit-confs, but can't find what to do instead.

I am very sorry if my questions appear to be beside the point, I am still learning and appreciate if you can help me understand what is happening.

What I have tried:

plex:
      image: ghcr.io/linuxserver/plex
      container_name: plex
      network_mode: host
    environment:
        - PUID=1000
        - PGID=1000
        - VERSION=docker
      volumes:
        - /root/Dockervolumes/plexVolumes:/config
      restart: unless-stopped

swag:
      image: ghcr.io/linuxserver/swag
      container_name: swag
      cap_add:
        - NET_ADMIN
      environment:
        - PUID=1000
        - PGID=1000
        - TZ=Europe/Frankfurt
        - URL=fermentedbeans.coffee
        - VALIDATION=http
        - SUBDOMAINS=fermented
      volumes:
        - /root/Dockervolumes/swagVolumes:/config
      ports:
        - 443:443
        - 80:80
      restart: unless-stopped

 myapp:
      build: .
      ports:
      - 5001:5001
      links:
      - swag
      - plex