I've set my Paypal IPN to accept the per item format so that customers will see each item they've purchased when they go to pay. It works fine using the aggregate method but when I set it to per item I get the following error; Anyone got any ideas as to what the problem could be or how I could even start debugging?
I don't know the exact answer to your problem, but you might want to check the OsCommerce forums. It's at http://forums.oscommerce.com/ Good luck - I have issues with Paypal on my osCommerce site as well, but of a different nature!
The first port of call when I had this problem was the oscommerce forums. There was nothing there that could solve my problem and I've found when I've posted over there that no-one actually answers your question - they just ask a hundred more questions of their own. I'm going to rip into the paypal_ipn.php file today and try and figure out which data isn't getting sent to paypal as it must be item specific data getting lost otherwise it wouldn't work when I change it to the aggregate system. Email me your problems with paypal and I'll see if I can give you a quote to fix it.