While doing some work on the AMPRnet hamnet.nu network, we needed to connect a UniFi box to the network, but it could not find the UniFi controller, so i used this command, top fix it. And assign where the controller is.
More info here, how to move a UniFi unit to a other Controller.
BusyBox v1.11.2 (2015-07-24 03:06:31 PDT) built-in shell (ash)
Enter 'help' for a list of built-in commands.
UniFi# set-inform http://192.168.1.10:8080/inform
Adoption request sent to 'http://192.168.1.10:8080/inform'.
1. please adopt it on the controller
2. issue the set-inform command again
3. will be saved after device is successfully managed