This plugin is a gateway between your ZetaPrints portal and PayPal Pro. Use it to accept credit cards directly on your website.
This plugin sits between your ZetaPrints portal and PayPal Pro. Users place orders on ZetaPrints and redirected to a certain page on your WordPress site to make a payment.
The page contains a form generated by the plugin. Users enter their credit card details and the transaction is processed via PayPal Pro API. The user gets a confirmation screen with success or failure message. At the same time, the plugin sends a message to ZetaPrints to confirm the payment. ZetaPrints updates order status and balance accordingly. In the end, the user returns to the list of orders on ZetaPrints.
This plugin was developed as an open source project and is hosted on Google Code. You are welcome to poke around and generally do as you please, as it's under MIT license. A more user-friendly explanation is on web-to-print help website.