the authorize.net settings require a Login and Transaction key.
the login is the value used for the x_login variable of the transaction. See the Authorize.net AIM developer page
AIM/
under Section Two - Submitting Transactions -> Minimum Requirements
3d secure is a service that offers an added layer of protection for credit card information:
3-D_Secure
to help determine why the transaction is failing, add the following code to the checkout_failure.php page:
<?php
@session_start();
echo "<p>Auth Net: <br />";
echo "Full Request: ".(isset($_SESSION['WAAuthNet_postedValues'])?htmlentities($_SESSION['WAAuthNet_postedValues']):"n/a")."<br />";
echo "Full Response: ".(isset($_SESSION['WAAuthNet'])?htmlentities($_SESSION['WAAuthNet']):"n/a")."<br /></p>";
?>