How to create a Zen Cart payment module

I'm interested in writing a Zen Cart payment module for a certain payment-gateway for people to download and install in their ecommerce website. My experience with Zen Cart is minimal so I don't know where to start. I checked the FAQ section on Zen Cart's website and I only found completed modules, no code examples of how to write one from scratch, or how to deploy 开发者_开发问答it. Could someone possibly give me some example code or teach me the basics involved?

Your best bet is to download other payment modules (there is a list here) and see how they work. Developing payment modules is such a specialized task that I doubt anyone has written documentation for it. I am sure you can find a module with well-documented source code.

Your approach really depends on the API/interface the gateway provides. If you look at the built-in Linkpoint module, it just uses cURL to communicate with Linkpoint. If you look at Beanstream INTERAC (in free software add ons), it uses cURL but it also expects a couple of callback URLs to be provided. There are other models too - your best bet is to get an understanding of what the gateway wants, and then look for an existing module that also uses this communication model.