The logic flow of FairPay is straightforward, and is as follows:

1. A PayPal transacton is sent to your flipna URL as configured in your PayPal account profile.

2. The web server (httpd) starts flipna.

3. The flipna program confirms the validity of the transacton with PayPal's servers.

4. The flipna program then writes an XML file into a spool directory, and then executes all commands listed in the commands file, in order. If the session count was exceeded for the configurable amount of retry time, the file is left in place. If all operations succeed, the XML file is removed after command execution.

   This command execution phase is where database population is achieved with fairpay_sql_populate or the program of your choice. You may insert other programs afterwards to handle "business rules" operations.