PayPal NVP/SOAT API was introduced several years ago. It enables people selling products in their own weibsite. Basing on this set of APIs, I also developed a tool, Digital Goods Express Checkout, with it, you can very simple integrate “Buy Button” in your website. No matter your website is created by WordPress, or Joomla, or just a plain HTML.
Nowdays, PayPal releases a new approach to integrate their Payment gateway through API. It’s called REST API. For different implementation, but with the same checkout experience, people can still sell their digital products on the website without any limitations.
If you are people who want to sell products and make money, you don’t need to know about the different. What you need to know, it’s probably about how to set it up in your website and start to sell.
For those people who want to develop tools or integrate the PayPal button in their own softwares, the PayPal provides a set of development documents.