I've come to test my new Zen Cart 1.3.8a but can't seem to get it to work with Paypal. Triple chekced what I've done in admin payment module using PayPal Website Payments Standard plus my PayPal buisness account (verified) and everything is correct. Contacted PayPal merchant technical support but they say it must be the cart as they always do!

Can anyone help as the problem is driving me loopy?