What are the ways to integrate PayPal (or other monetizing service) into an Adobe AIR desktop app?

Hey all

I just finished publishing my AIR mobile app for iOS and Android, both featuring freemium style in-app purchasing/billing, for a single purpose only - opening the app to be full featured.

Now the client wants a desktop version of the app. I need a way to monetize the same way: the user wants all the features - they click a button in the app, pay the 2 dollars, and now all the features are accessible.

I think going out to PayPal, paying there and returning to the app would be best, but I cannot get the files I found here to work.

Do you have any suggestions of a workflow with examples, or a service with AS3 support?

thanx