@Annex2022 It's important to check if the server can communicate with the Router's LAN IP. Try to Ping the server IP on the router page-->Diagnostic. 

TP-Link has an article about this issue you may refer to https://www.tp-link.com/us/support/faq/2980/  

Aha, that did the trick, Java needed to be manually unblocked in the firewall. Thanks!

And kaboom! What should have been super smooth and easy blew up. So the router became adopted according to itself. When accessed via IP address it would say its managed by the controller with only option to reset to factory defaults. In the controller it would say its Adopting (not adopted). The controller imported the WAN settings correclty, but it didnt import the LAN settings, instead it exported the LAN settings to the router and thus changed it from its pre-configured 10.0.0.1 to 192.168.0.1. Updating the LAN gateway/dhcp in the controller would not update the router, even after power cycling it.

So I reset the router back to factory defaults, and once it re-appeared in the controller I clicked on adopt. This time within about 30 seconds a message would come up saying "device does not respond to adopt commands". Fantasticly useless software at this point, so I re-configured the router in standalone mode (I really wanted to test out the OpenVPN which is the only reason I tried the controller) and will leave it as is. Massive Ubiquiti flashbacks from 5+ years ago here, very disappointed.