I have been sing a php interface to PayPal to test credit card transactions on a web site. It works fine, but I find out now that it's what PayPal calls the "Pro" methods & will cost them more.
One alternative is described here: https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/e_howto_api_ECGettingStarted
In the section entitled "Testing an Express Checkout Integration", about half way down it talks about "Review the response string from the SetExpressCheckout API operation.". It is not clear to me how this response string is passed back to the "RETURNURL" page.
Can someone clarify?