It will definitely need to be the public IP address.
I would check that you don't have any firewalls blocking the HTTPS request inbound to your Clearpass server and if that is all ok, check the Event Viewer on Clearpass to see if there are any events highlighting that the requests are being dropped.
You can run a packet capture from Clearpass (Administration -> Server Manager -> Server Configuration -> Collect Logs) which would allow you to see whether Clearpass is receiving the HTTPS packets.
Also, if you haven't already log out of the whole system in appviewer and log back in. This may help.