wojodesign/simplecart-js — pull request #208 by napernik (2012-02-14 09:51:31+00:00)
Title: Adding "invoice" field to PayPal checkout

Using "invoice" field allows using implementing custom invoice handling functionality. Once the field is present, PayPal does the following:
1) makes sure that the same invoice will not be payed twice
2) sends "invoice" field back in "payment data transfer" and "instant payment notifications", so it is known which invoice is payed