on the pp_checkout_failure.php page, add the following code after the <body> tag:
<?php
if(!session_id()) session-start();
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 /></p>";
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>";
?>
this will write the full request and full response from the gateway to the page for troubleshooting.
NOTE: The full request and full response will contain sensitive information that should be removed before posting here.