I honestly didn't know that. I personally just configure a specific port for each stack and have NPM forward it directly without configuring any network.
I just noticed OP did configure a network, but tbh I don't know how they work exactly and gave recommendations on what I knew.
If using networks is the standard way or OP feels better off that way then I'll leave them to it
I've just noticed: you've set your forward hostname/IP to audiobookshelf. That should either be your PC's IP address (if you've set up a static one in your router's panel) or its hostname. Unless you've named your PC audiobookshelf it still won't work.
I'm pretty sure you have to specify a different port. Audiobookshelf uses port 80 by default - which is already taken by NPM - and since you're not mapping it to any other port those services will conflict.
Map the port to something easy to remember in the compose file. Not only is it required in your setup but it is good practice. If you have to manage a lot of services, it is hard to keep track of all the ports they use if you keep them on their default values. I personally chose a port range (like 12300 -> 12399) and map all of my services respectively (Komodo to 12300, Authentik to 12301, etc.).
Also remember to update the port in your NPM config.
TL;DR: Audiobookshelf's default port is 80, which conflicts with NPM. Change it.
Goated dev