Amazon Flexible Payments Service (FPS) Part I, An Overview

Amazon Flexible Payments Service (FPS) is a set of web services that allow developers create applications to move money from one entity to another. Payment can be in the form of credit cards, bank account , or Amazon Payments balance.
Requests can be made either via SOAP or REST. In my case I had to use REST because Mono (.Net on Linux) has not implemented WSE 2 or WSE 3.
Another important feature to be aware of is Instant Payment Notification (IPN). This frees up a developer from having to implement a scheduled job that queries Amazon FPS for completion of payments. Because IPN will push (publish) a response to your listening website/webservice for you.

References:
Getting Started Guide: http://docs.amazonwebservices.com/AmazonFPS/2007-01-08/FPSGettingStartedGuide/
Developers Guide: http://docs.amazonwebservices.com/AmazonFPS/2007-01-08/FPSDeveloperGuide/