If NGINX proxy manager is a docker container on the same machine as your other services you can point it to 172.17.0.1 and then the port number. And then the domain can be duckdns or whatever you’re using without the http.
Edit history
If NGINX proxy manager is a docker container on the same machine as your other services you can point it to 172.17.0.1 and then the port number. And then set the the domain can be duckdns or whatever you’re using without the http.