PayKickstart allows you to setup tracking IDs to the end of your checkout and affiliate links.
This is particular handy for when you are running multiple promotions for a product in many places, such as Facebook, websites, or an email list. It will allow you can keep track of where your traffic is coming from by using tracking IDs.
Take your affiliate link and add ?tid= then whatever the traffic source is. For example:
You can monitor your traffic and sales metrics under “Reporting” >> “Sales” or “Traffic”.