Unable to correctly serve sub-paths using Nginx Proxy Manager

Checklist

• Have you pulled and found the error with jc21/nginx-proxy-manager:latest docker image?
  • Yes
• Are you sure you're not using someone else's docker image?
  • Yes
• Have you searched for similar issues (both open and closed)?
  • Yes

Describe the bug
I am trying to set up services under sub-paths (e.g., https://mydomain.com/service1) using Nginx Proxy Manager (NPM). While subdomains work fine (e.g., service1.mydomain.com), sub-paths don’t seem to function correctly.

For example, I have configured https://mydomain.com/proxy to forward requests to http://nginx-proxy-manager:81, but when trying to access the service, the resources (CSS, JS, etc.) are still being requested from the root path (https://mydomain.com/) instead of https://mydomain.com/proxy/.

I have tried using custom locations, sub_filter, and proxy_redirect configurations, but the resources are not loading properly from the sub-path.

This issue seems to be similar to what others have experienced in discussion #1288 and this Reddit post, where sub-path forwarding doesn’t work as expected in NPM.

Nginx Proxy Manager Version
v2.11.3

To Reproduce
Steps to reproduce the behavior:

1. Create a proxy host for https://mydomain.com/proxy.
2. Set it to forward to http://nginx-proxy-manager:81.
3. Access https://mydomain.com/proxy in the browser.
4. Check the console for resource loading errors (404 Not Found).

Expected behavior
Resources (CSS, JS, etc.) should load from https://mydomain.com/proxy/ and not from the root path.

Screenshots

This works.

But this doesn't work.

Operating System
Docker on Linux

Additional context

• I have tested this with custom locations in NPM.
• Also tried adding sub_filter rules in Nginx to rewrite resource URLs and using proxy_redirect to ensure any backend redirects retain the /proxy prefix.
• Subdomains work fine, but sub-paths present this issue.
• Docker version 24.0.5, build ced0996

No repository file or test is named. Reproduce the proxy-host setup in the issue, inspect how Nginx handles /proxy and browser requests for CSS and JS, and compare it with the working subdomain case. Done means the proxied service and its assets load under /proxy/ without root-path 404s.