So I read around the forums a bit and found a few posts from people about using nzbget behind a reverse proxy (most use nginx) and it got fixed in an update eventually, but for me it's not working when I use traefik as a reverse proxy (radarr, sonarr work fine btw).

In nzbget it says "Web-Server: 400 Bad Request, Resource: //xmlrpc"

Anything I can do to fix this?

Nevermind I changed it from subdir to subdomain and that works fine, probably has to do with a rewrite rule or somethign that is missing.