Nginx Proxy Manager without a domain?

[Adephx]

I have Frigate container running inside an isolated network on port 5000, together with Nginx Proxy Manager, that has its port mapped to the main network, so that it can be accessed freely (192.168.66.39:81). How do I use Nginx Proxy Manager to redirect connections from 192.168.66.39:5000 to frigate:5000?

I tried mapping the port 5000:5000 in Nginx Proxy Manager compose, then added a proxy host with source: 192.168.66.39:5000 and target: frigate:5000, but that doesn't seem to work.