Amazon Web Services provides developers with another option for payment processing. Their Flexible Payments Service (FPS) is slightly more complex than the Google Checkout API, but also offers some additional robustness. It uses a significantly different technical approach, however, and will require some adjustments to our payment processor designs.
FPS allows developers to create more advanced payment mechanisms, as well. For example, you can use FPS to set up recurring payments, such as subscriptions, as well as single-click payments whose parameters will be remembered over time. Google Checkout API offers similar advanced functionality. These features of both services will not be implemented here, but are well documented on the Web. Later in this book we will discuss using Amazon's payment services for digital goods, such as music and software.
The FPS uses a similar interaction flow to Google Checkout. We present our customer with the full contents of their shopping...