Connecting the Containers
HTTP Proxy for Arr Services
Transmission, qBittorrent, and Deluge all have a HTTP proxy that will route requests through the VPN connection.
You can configure other apps to connect to these containers proxy services by using transmission:8888, qbittorrent:8118, or deluge:8118, depending on which you are using.

Connecting the Containers to each other
When connecting containers together such as Prowlarr to Sonarr and Radarr or Sonarr/Radarr to Overseerr etc, you can use the name of the container (e.g. prowlarr or radarr) and then defining the container port to connect to (e.g. prowlarr:9696 or radarr:7878).
For the names and port of each container to use, get the Container Name and Container Port values from the Container Map.
Here's an example within Prowlarr:
