I purchased a bunch of USW-Flex-Mini switches. They are part of the Unifi ecosystem so they are managed by a controller that I have running in a docker container in a server in the house. Whenever I have plugged in any other Unifi device, they showed up for adoption by the controller without any issue. But not these switches.
They booted and got their addresses by DHCP as expected. With Unifi devices, typically you can SSH into them and specify whey they IP address and port they should inform so they can be adopted. Of course, these switches don’t have SSH access.
The Unifi USG I use provides DHCP and a lot of the documentation and posts on these switches mention “DHCP Option 43”. There is no way to specify this DHCP option in the DHCP service on the USG.
In the legacy web UI, go to Settings -> Networks. There should be a LAN, edit the LAN the switches are connecting to. Scroll to “DHCP Network application” and enter the IP address of your Unifi controller.
In the new web UI, go to Setting -> Networks. Select the device the switches are connecting to (in my case, the USG). Scroll to “DHCP Service Management” and click on “Show Options”. Scroll to “Option 43 Application Host Address” and enter the IP address of your Unifi controller.
Once this was done, power cycling the switches had them correctly inform to the controller and I was able to get them adopted.