Originally Posted by BigFurry

You could probably look at your browser cookies for the paysite's and the NATS program's domain, and find the one that is used for tracking.

But it's a lot quicker and I think more reliable to test by:
- going to the paysite's join form
- submitting a user/pass
- go to NATS and see if the submit was counted

Personally I can't remember ever encountering tracking problems with NATS though.