How I solved UniFi AP adoption failed error

Recently, out of the blue, one of my U6 Lite access points stopped working. In the UniFi controller, I saw the “Adoption failed” error.

As a skilled IT professional, I tried the classic solution: turning it off and on again. Guess what? Same error.

The next step was to factory reset the device. I SSH’d into the device and ran:

$ syswrapper.sh restore-default & set-default

After what felt like an eternity, the device popped up in the UniFi controller, ready to adopt, and this time it worked. I assume that using the physical button to reset the device would have done the job as well.