This is a kind of "developer's log" that should be helpful to others who want to integrate PayPal Website Payments Pro into their own e-commerce solution.

When deciding upon a merchant account provider consider this about PayPal Website Payments Pro:

• PayPal WPP works only with U.S. customers.
• Some people claim PayPal WPP has a much lower card acceptance rate than traditional merchant accounts.

From the point of view of many entry-level merchants, WPP is the killer merchant account service. Not only is it considerably less expensive than traditional internet merchant accounts, it is easier to use, and it doesn't have the kind of fragmented pay flow that traditional merchants accounts suffer from, where the gateway provider is a different company and different system than the merchant account provider, which is different from the integration provider, with each company charging a healthy fee each month.

I've worked with a couple different merchant gateway systems, and PayPal Website Payments Pro is, by far and away, the most difficult to implement. Most payment gateways method of payment capture involves putting together an HTTP POST query with the customer's payment details, sending it to the gateway over SSL, and then retreiving and parsing the results from a simple format. However, WPP uses SOAP, and requires that you aquire a digital certificate from PayPal, and it requires that you also implement PayPal's "Express Payment" option in additional to the "Direct Payment" option that is more like traditional merchant accounts. To make it more difficult, the documentation is spread all over the place, and you have to visit and register for additional PayPal sub sites.

To be continued...