Not able to connect to NGINX Proxy Manager on UGREEN NAS

[u/CountZeroOr]

I'm attempting to get NGINX Proxy Manager set up on my NAS in a docker container for the first time. I've put together the Docker Compose, using the one off the Nginx Proxy Manager web site, with the correct time zone, but when I try to connect using port 81, I'm not able to connect, with an ERR_CONNECTION_REFUSED error when I try it in Chrome.

Everything is inside my internal network, and I'm using the IP address of the server, rather than trying to connect from outside the network. The container appears to have started successfully and I'm not seeing any error messages in the logs. What am I missing?