How do I use my PayPal account?

PayPal has about 8 different APIs that work in basically two different ways.

Direct Payment works like a traditional gateway. You submit the card holder, credit card information and payment information and get a response, accepted or an error message.

Express Payment works by allowing a PayPal user to pay for a transaction using information stored at PayPal's site. The transaction is started on a merchants "web site" (or Android device, in this case) and completed on PayPal's web site. Express Payment makes a lot of sense in a web based shopping cart. It makes very little sense for use in Merchant for Android, since most of the transaction happens in a browser.

Direct Payment is only possible via Website Payments Pro and Payflow Pro, so those are the two APIs that are implemented in Merchant for Android.

All of the other PayPal APIs, such as Website Payments Standard or "Regular" PayPal, support only Express Payment.