Building a payment gateway plugin

Page under construction. Steps I (Mike M) went through to teach a guy (Brad R) how to build a payment gateway plugin.

The four components of a payment gateway

1. payment_options.php - Place in sitebuilder admin tool where webmaster fills-in gateway account id and whatever other data is required by the gateway, and can choose your gateway as the primary credit card processor to be used in his website checkout process.
2. pgm-checkout.php - Outputs payment option choices to website visitor based on what webmaster sets in Payment Options
3. pgm-payment_gateway.php - Passes the checkout order data to the gateway.
4. pgm-show_invoice.php - Catches response from gateway and directs website customer accordingly to final invoice (on success) or failure page if payment attempt did not succeed (e.g., because of declined credit card, etc.).

pgm-checkout.php

1. Add condition check to output hidden PAY_TYPE form/field if your gateway is set as the primary credit card processor in Payment Options
2. Add check for your gateway to condition that determines whether to show credit/debit card payment option to website visitor if one of the defined (checked for) credit card gateways is choosen in Payment Options.

pgm-payment_gateway.php

This is the script that .