'Service Classification failed' means that you didn't have a matching service defined in the ClearPass services.
From the log, you can also see that the incoming request is of the type WebAuth, and you don't have any WebAuth services defined.
Did you follow some integration guide? From this point, I would add a WEBAUTH service and see what comes into ClearPass then,
What is not clear to me is how the actual authentication will happen in this situation. There are basically two methods for guest authentication. First is where the access device will do a RADIUS authentication against ClearPass, second is where the client will do a WebAuth against ClearPass and ClearPass then sends a RADIUS CoA (Change of Authorization) to the access device to allow traffic. This last method is often combined with a MAC authentication.