Adopting UniFi Flex Mini
Flex mini switch has 5 ports 1st port is PoE IN support 802.3af and it is powered by a 5V, 1A Power Adapter available inside the box which is USB type C.
Adopting a flex mini switch is different from all other UniFi devices as it doesn't support SSH so you have to adopt them via DHCP option 43 or local discovery L2 method.
Local controller L2 discovery method (Recommended)
NOTE You should have a local UniFi controller running (Or install controller on the local network) in this method and make sure the switch is connected to Network and powered.
Go to settings >> controller >> enable Make controller discoverable on L2 network and apply the changes.
Go to the devices tab and the Flex mini should be discovered with as status of “Pending Adoption”.
After adopting into local UniFi controller you can migrate a site to Cloud Unifi and move the devices to specific sites for a site migration you can follow this guide
After migrating the temporary local site to Cloud Unifi you can move it. Click on switch >> go to config >> manage device >> under forget device there is an option to move the device. After the move has completed, it will be connected to your final destination site.
DHCP option 43
Once you powered the switch and connected to the LAN network, you will have to enable DHCP option 43 on your Router LAN network.
Follow this guide to enable DHCP option 43
Once it has been adopted to the controller, go into settings>controller>controller settings, where it says Controller Hostname IP input your hosted controller name (example.cloudunifi.com) and check the box that says "Override inform host with controller hostname/IP". Your devices will replace the IP assigned to the inform URL with the domain name of your controller, but it may take 5-10 minutes.