1 - VX and AAP licenses should be valid on the controller
2 - If applying the VX license using this command : #license VX and getting an error then the key might have been created when the VX had a different IP address. When the IP address on the VX controller is modified, the serial number changes and this disables all licenses. If this is the case, recreate the license/s using new serial number. Type VX in upper case when running the licensing command.
3 - Make sure the AP can ICMP and Mint ping the controller and vice versa
4 - Make sure ports 24576 and 24577 are not blocked
If above are successful proceed with one of these adoption methods:
https://gtacknowledge.extremenetworks.com/articles/Solution/CLI-command-for-layer-3-adoption-of-acce...
Christoph S.