Some questions:
- What is your Clearpass version 6.7.x or 6.6.x ?
- What is your 3810 switch firmware ?
CPPM > Configuration > Network > Devices
Be sure you use the correct Vendor Name in your NAD configuration.
I make the mistake before that the Vendor Name isnt Aruba but HP Enterprise.
On your switch configuration be sure that you configured this:
radius-server host "ip-clearpass" dyn-authorization
Iam not 100% sure but i think it was firmware release 16.04 is needed to do this.