Ok so the APs are on a different subnet to the controller. Whatever discovery protocol they are using does not work between them which is not surprising.
The easiest thing might be to put the APs on LAN temporarily, adopt them to the controller and then mover them back. As long as they remember the controller IP and you have rules to allow the APs to reach the controller IP and port on the wifi interface that should work.
If they don't remember you can pass the IP to them via DHCP option 138:
Or you can just configure the controller IP via the EAP discovery tool: