add the following code to the cehckout failure page:
<?php
if(!session_id()) session_start();
echo "<p>Direct Pay: <br />";
echo "Full Request: ".(isset($_SESSION["PP_DirectPayment_postedValues"])?htmlentities($_SESSION["PP_DirectPayment_postedValues"]):"n/a")."<br />";
echo "Full Response: ".(isset($_SESSION["PP_DirectPayment"])?htmlentities($_SESSION["PP_DirectPayment"]):"n/a")."<br /></p>";
echo "<p>Express Authorize <br />";
echo "Full Request: ".(isset($_SESSION["ECO_Auth_Request"])?htmlentities($_SESSION["ECO_Auth_Request"]):"n/a")."<br />";
echo "Full Response: ".(isset($_SESSION["ECO_Auth_Result"])?htmlentities($_SESSION["ECO_Auth_Result"]):"n/a")."<br />";
echo "<p>Express Process: <br />";
echo "Full Request: ".(isset($_SESSION["ECO_Process_Request"])?htmlentities($_SESSION["ECO_Process_Request"]):"n/a")."<br />";
echo "Full Response: ".(isset($_SESSION["ECO_Process_Result"])?htmlentities($_SESSION["ECO_Process_Result"]):"n/a")."<br /></p>";
echo "<p>UPS: <br />";
echo "Full Request: ".(isset($_SESSION["hbCart_UPS_FullRequest"])?htmlentities($_SESSION["hbCart_UPS_FullRequest"]):"n/a")."<br />";
echo "Full Response: ".(isset($_SESSION["hbCart_UPS_FullResponse"])?htmlentities($_SESSION["hbCart_UPS_FullResponse"]):"n/a")."<br /></p>";
echo "<p>FedEX: <br />";
echo "Full Request: ".(isset($_SESSION["hbCart_FedEx_FullRequest"])?htmlentities($_SESSION["hbCart_FedEx_FullRequest"]):"n/a")."<br />";
echo "Full Response: ".(isset($_SESSION["hbCart_FedEx_FullResponse"])?htmlentities($_SESSION["hbCart_FedEx_FullResponse"]):"n/a")."<br /></p>";
echo "<p>USPS: <br />";
echo "Full Request: ".(isset($_SESSION["hbCart_USPS_FullRequest"])?htmlentities($_SESSION["hbCart_USPS_FullRequest"]):"n/a")."<br />";
echo "Full Response: ".(isset($_SESSION["hbCart_USPS_FullResponse"])?htmlentities($_SESSION["hbCart_USPS_FullResponse"]):"n/a")."<br /></p>";
?>
this will give the full request and full response from the gateway to help uss determine what the problem is.
NOTE: The full request and full response will contain sensitive information like Credit card numbers and paypal api account information, you will need to remove any sensitive information before posting it here.