It took me a while to figure this out.
I have an Orbi (mesh) router hooked up to my Cox router. I have my iMac (where Channels server is) hook up to my Orbi satellite using both Wifi and Ethernet. (I wanted just to hook up Ethernet but syncing with other Apple devices like an Apple Watch gets funky.)
Changed Channels to Manual port forwarding. It gave me the IP of my iMac Ethernet 192.168.1.38 (rather than the Wifi which is 192.168.1.39). Okay, so I forwarded 8089 from my Cox to Orbi and then Orbi to my iMac (IP assigned to my Ethernet connection).
Tried watching Channels on my iPad using LTE (to simulate Away from Home), and I kept getting an error that port forwarding was not set up properly. Okay, so I changed the port forward to iMac using the IP for my Wifi (192.168.1.39). No surprise...didn't work.
Then I remembered something...I unplugged my Ethernet and started from the beginning. Channels is now saying to forward to my Wifi IP 192.168.39 (Wifi on my iMac). I did the port forwarding again and IT WORKS.
I then plug back in my Ethernet cable to my iMac. Interesting enough, Channels is now saying to forward to 192.168.1.38 (ethernet) again! However, it is working so I am not changing anything.
Anyway, bottom line...if having trouble and you are connected via Wifi and Ethernet, unplug the Ethernet and give it a try!