NPM Proxy Presents NPM Login

[Leetxjd]

I must be doing something wrong and I am hopeful someone may provide some insight.

I have a dynamic dns through Dyndns.com and have a Let's Encrypt SSL cert for the domain. I have installed NPM on TrueNas Scale as an app. I have entered the domain in the appropriate domain field and the forward hostname and port for an internal app (NextCloud if that makes a difference). I have set my router to port forward to port 80 and 443 on the server with NPM (and I have reset my Nas login to listen to port 81).

All this results in is the web browser bringing up the NPM Login page instead of NextCloud. I am stymied as to why this might be the case. I'm certain I have some sort of misunderstanding about the NPM setup, but I have been unable to figure out the issue.

Any insight would be most appreciated.