If you use PayPal Website Payments Pro (WPP) for Zen Cart version 1.3.9 up to version 1.5.0, you may be suffering from a bug where some error messages, particularly processor declines, are not displaying to your customers in the checkout. This results in the customer being directed back into the checkout without indication if their payment was processed or not. This causes a lot of frustration and many customers will continue to try checking out until Zen Cart times them out for making too many failed attempts (again, no message is shown; the ZC developer’s claim this is for security reasons and is deliberate), or they think that they are going to double charged and either leave the site or contact you to check.
The bug is related to code in the WPP module. Fortunately, there is an easy fix. If you go to ADMIN->MODULES->PAYMENT->PAYPAL WEBSITE PAYMENTS PRO and set the option DEBUG MODE to anything other than “OFF”, all error messages will start to display in the checkout.
We’ve notified Zen Cart of this bug and hopefully they will fix it in their next update or release a patch. In the meantime, implement our temporary solution and you will be doing your customers, and yourself, a world of favors.