If you are trying to understand the eBay communication APIs, then you have commited yourself to a BIG leaning curve.
As I have walked the walk already(I worked for eBay), I hope my experiences can help those who follow me up this monumental path..
All eBay programming APIs are designed to talk to the exposed eBay services. These services are constantly evolving. As they evolve, older versions become obsolete.
These older version are usually supported for about 14 months after a new version is created, however, they will eventually fall off the supported list and start to cause API call failure.
So to make sure you can design applications that talk correctly to the eBay services, you need an uptodate API.
FYI: you will need to keep your API up-to-date as well duing the lifetime of your application. As the APIs are really a communication layer, you should be ok calling them directly, rather than implementing your own abstraction layer on top.
So far we have managed to find one fully functional PHP API.
You can get this from IN TRADE SYS at this url:
http://www.intradesys.com/index.php?id=ebay_at_for_php&L=1.
These guys seem to be totally up to date with the current version of the eBay services platform. They also provide a few samples and some basic documentation...
Definetely Recomended if you are looking to develope eBay applications with PHP.
