Looks like I'm going to have to sort this out myself, unless I have better luck on the phone tomorrow. I called PayPal tonight, but the two techs that I talked to, aren't familiar enough with integration. I'll try calling during the integration team's hours (7-4 Central). I'll try to take notes as I go, and save someone else some time. Here are some raw notes that I've made so far:
What types of integrations are available?
If you're building your own shopping cart or storefront, start with the HTML overview of PayPal Payments Standard (formerly known as Website Payments Standard).
Or you can jump right into the Standard Variable Reference, which provides reference information for all the relevant HTML variables.
This type of integration allows you to create and manage buttons within your own application. It is often used by developers who provide shopping carts for merchants. To get started, go to the Button Manager API overview.
profile > My Selling Tools > API Access > Option 2
API Username XXX
API Password XXX
Request DateMar 18, 2014 16:16:39 PDT
Accept payments from your online stores before setting up APIs
Enable Express Checkout to accept payments from your online stores right away. You can set up API permissions or credentials later.
PayPal API Concepts and Terminology
* Specific API services that allow you to make payments, refund payments, search or view transaction data, and more.
* A PayPal-generated unique digital signature, such as a line of text or hash marks, that you copy from the PayPal website and use with your API username and password when making a call. An alternative to the digital signature is the API certificate; if you’re developing a custom solution with PayPal APIs, we recommend this option.
* A file that you download from the PayPal website. The API certificate, an alternative to an API signature, is used with your API username and password when you make API calls. The API certificate is a text file that must be readable by your application each time an API call is made.
API username and password
* A PayPal-generated name and password that identify you when you make API calls. The API username and password are different from your PayPal login username (email address) and password.
* Your API signature, API username, and API password together are called three-token authentication.