I did ask somebody that does this already, but this answer wasn't clear enough for me.
"You would need to find a 3rd party solution, and then integrate it into your program. I
use a custom script that my programmer wrote for me, but I know that there are many commercial products available for this."
My question is HOW do you integrate it and how does the serial number come up on the thank you page?
Any help would be appreciated.
Also, would changing my program to offer a trial version affect my affiliates and their commissions?