I might be wrong with this suggestion, but it appeared to me you might have more chance to have your problem solved at the PHP forum. I once had an osCommerce webshop which I customized, so I remember some things about how a webshop is organized. As far as I remember the buying process involves interaction with the server and is handled by PHP. Of course HTML is used also for text that is displayed on the computer screen. Reading back my own comments, I think to start with it would be useful if you copied the code you or at least PayPal suspect to cause trouble (one line and a new line to insert ...).