This will guide you through the setup of the UniFi ac Lite AP.

• Plug in Access Point using PoE injected ethernet

• Install Controller Software either on Raspberry Pi, Unraid Docker, actual hardware cloud key, etc.
• Connect to Controller Software.
• Adopt Access Point
• Device Name: BrimAP

• Site
  • Site Name: Default
  • Rest of settings are self explanatory
• Wireless Networks
  • Add networks as desired
  • WPA Personal Security
• Admin
  • Add New Admin
• Controller
  • Name: Brimblecom AP
  • Hostname: unifi.brimble.com

• I had a couple instances where (i guess after playing with PiHole maybe? I dunno) it would get stuck in adopting mode. This post here https://community.ui.com/questions/UniFi-is-stuck-at-Adopting/596ee99e-5828-4fa2-930d-e6d3b68deba6 by EricE had the answer.

  Want to solve it permanently?  Ensure your controller computer has a DNS resolvable hostname on your network(s) (you can ping it by name from your Unifi devices) then go into Settings on you controller, go to the controller section and ensure that your host name or IP address for your controller are entered intot he Controller Hostname/IP field, then check the Override inform host with Controller Hostname/IP like so: 
  
  
  If you don't also check the Override inform host with Controller Hostanme/IP box too, nothing changes.  You have to do both - enter the hostname or IP addres and check the box!
  
   
  
  Nine times out of ten when APs can't find the controller, your DNS is not pointing unifi to the IP address of the Unifi controller.  By default the AP's fall back to trying to resolve the DNS name of unifi and if you can't issue a 
  
   
  
  ping unifi
  
   
  
  from a command line on one of your APs you have ssh'd into and have it successfully resolve to your controller, that's your problem.  Ensuring your IP address is in the field and checking the box should solve it if you can't control the DNS that is serving the AP's.
  
   
  
  Also if your controller has more than one NIC configured, you will have a lot less issues adopting any Unifi kit if you ensure the override is enabled.  I learned that one the hard way 😛