A couple of things:
- if you are using a VIP on the ClearPass cluster make sure you add that in the list RFC server under the AAA profile
- make sure that the shared key in RFC server on the controller is correct
- on the controller check what's your NAS IP address by running this command :
show radius nas-ip , that IP address needs to be added to list of nad devices in ClearPass
- in clearPass make sure that when you the controller as a nad that you enable CoA
- if there's a firewall in between the controller and ClearPass you need to allow port 3799