We deploy a lot of Unifi devices for our customers and adopting them into our controller software can be a bit quirky sometimes. The two GUI tools that we are aware of to discover and adopt the devices,  Unifi-Discover (gets installed with the controller software) and Ubiquiti Device Discovery Tool (available as a Chrome App), seem to be hit or miss.

What I’ve found to be the easiest and straightforward way to perform the adoption task is to just SSH into the device and issue the proper set-inform command.

There a couple things you’ll need to know ahead of time:

1. SSH authentication is enabled in your controller (see screenshot below).
2. The IP address of the device – This can be found by issuing an arp -a command from the Windows CMD prompt or by using an IP scanner tool to find the IP address of your device by using the MAC-ID. By default the devices are set to DHCP out of the box.
3. The device credentials – If the device is factory defaulted, then the username is ubnt and the password is ubnt. If your device is not factory defaulted, then you can obtain your device credentials by navigating to the Device Authentication section of your controller Site Settings.
   

One you have the IP address and the credentials, open your favorite SSH client and establish a connection to your device using the discovered IP address and the proper credentials.