If you have PostAffiliate Pro 4 (PAP4) installed, you can integrate it with nBill to track purchases made through nBill by installing this extension. All you have to do (apart from adding the PAP tracking code to your template) is install the extension, and enter the path where you installed PAP (by going to Extensions->PAP on the nBill menu after installation). Every payment you receive through an nBill payment gateway will then be registered through PostAffiliate Pro, and if the payment was initiated by a computer with a PAP cookie, the commission will be awarded to the referring affiliate.
This is an nBill extension. Use the extension installer in nBill to install it.