Zencart version: v1.3.9h
Just signed up with Paypal Payment Pro and installed both Pro and Express today using directions found on the Paypal Express Checkout and from the Zen Cart book I bought. I also had a customer get the same 15008 Invalid data message. I called Paypal and they told me it is a programming error and not from their end. I have researched this and I have found nothing to fix this. I'm concerned that I put all my faith in paypal and my first transaction is a problem. Am hoping someone that reads this thread will have an answer. I also did a goodle search and it appears to be a common problem.