I have added a payment gateway for my zen cart. the problem is that once i complete the final step (step 3) to confirm the order, it just returns to the step 2 rather than displaying a error message or success message. but in the address bar it shows the error

index.php?main_page=checkout_payment&error_message=There+has+been+an+error+proce ssing+your+credit+card.+Please+try+again.
how do i get it to show in the checkout page ??