Tokens are unique identifiers for the payment instructions that have been installed in your FPS account or the accounts of third parties. We will use the terms “token” and “payment instructions” interchangeably to describe a set of payment rules that have been approved and are available for use in transactions. The FPS API provides operations to install, retrieve, and manage tokens in your account.
To perform transactions with FPS, you must install payment instructions that allow your application to act as a caller. In other words, you must create a caller token. Any FPS application must be able to access one or more caller tokens to perform its work. If you will be receiving payments through FPS, you must create a recipient token to authorize these transactions; you must also create a sender token if your application will send payments.
For the time being, we will focus on the most common and simplest example of an FPS application, one that accepts payments from customers by performing the transaction and receiving the resulting funds. This kind of application acts as both a caller and a recipient. For a discussion of applications that act only as callers that relay funds to third-party recipients, see Micropayments with FPS” in Chapter 12.
To install payment instructions using the FPS API, you must define your payment rules using the Gatekeeper language. This language is quite expressive and allows you to write very powerful rules, ...