Pihole web GUI will not load behind reverse proxy (NPM)

GUI does not load behind reverse proxy

Hi all, recently spun up Pihole via Docker and it works great! ...Except when accessing behind a reverse proxy. All GUI resources fail to load with a 502 error. I use Nginx Proxy Manager to proxy to pihole.local.mydomain.com with the following configuration:

    location / {
      proxy_pass http://PiholeIP:PiholePort/admin/;
      proxy_set_header Host $host;
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_hide_header X-Frame-Options;
      proxy_set_header X-Frame-Options "SAMEORIGIN";
      proxy_read_timeout 90;
    }
    location /admin {
      proxy_pass http://PiholeIP:PiholePort/admin/;
      proxy_set_header Host $host;
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_hide_header X-Frame-Options;
      proxy_set_header X-Frame-Options "SAMEORIGIN";
      proxy_read_timeout 90;
    }

The website is accessible, but no GUI elements are available. Has anyone run into a similar issue? I've reviewed a number of threads so far, but most of the issues seem to be about accessing Pihole from behind a reverse proxy at all, not that the GUI fails to load once accessing it.