Express Checkout - what it is and what it is not

Zen Cart and PayPal Express Checkout vs Website Payments Pro and PayPal Payflow Pro

PayPal Express Checkout
Express Checkout allows customers to pay quickly by bypassing the normal checkout process.
To use Express Checkout on your site, you simply need Zen Cart v1.3.7.1 (or newer) and a PayPal "business" or "premier" account.
In your PayPal account console, you have a "Profile" tab, under which you can obtain your required API Credentials. Enter them into the module, and you're ready to process.
Instructions on getting your API credentials and setting up your account, etc can be found on our PayPal partners page, here.
You can click here to see more about how PayPal Express Checkout works in Zen Cart.

Website Payments Pro
Zen Cart v1.3.8 or newer must be used if you wish to offer Website Payments Pro support (ie: specifically the ability to collect Credit Card data on *your* site and send it to PayPal for authorization --- all without sending the customer over to the PayPal site to use their PayPal account to login and pay you).

NOTE: Website Payments Pro requires payment of a monthly credit-card processing fee, billed to your PayPal business or premier account. Further details available on the PayPal Website.

PayPal Pro / Payflow Pro
Zen Cart does not include PayPal Pro, which some may recognize as the former Verisign "Payflow Pro" option of processing Credit Cards via their payment gateway. BUT ... there is an addon for it. If you need this, you can grab the PayPal Payflow Pro module from the contributions area.

NOTE: PayPal/Payflow Pro requires payment of a monthly credit-card processing fee, along with a setup fee. Further details available on the PayPal Website.