I wasted plenty of time fighting with adoption. Resetting to firmware, retrying adoption via SSH and Smartphone L3 over and over. It wouldn't show up as available for adoption on the site I needed it on. I found it was hiding in the default site list, as an offline device. I had to forget it/move to the site I want to be in. Grr!
Open port 8080/tcp in the firewall on the controller device, than SSH into the UAPs and set-inform to the controller.
USG-XG-8 • USG-4-PRO • USG
US-XG-16 • US-48-500W • US-24-POE-250W 2x • US-16-POE-150W 3x • US-24 • US-8-150W • US-8
UAP XG • UAP-SHD • UAP-HD • UAP-NanoHD 2x • UAP-AC-PRO 2x • UAP-AC-LITE • UAP-AC-IW • UAP-AC-M • UAP-AC-M-PRO 2x
UAS-XG • UCK-G2-PLUS • UCK-G2 • UCK