Adding Field to Checkout

[vandiermen]

Need to add fields onto the checkout payment page
......
it wont populate in my database.

Kuroi gave answer on page 1. To clarify:

EDIT
includes/modules/pages/checkout_confirmation/header_php.php

FIND
$_SESSION['comments'] = $_POST['comments'];

ADD under it

if (isset($_SESSION['frequent_code'])) {$frequent_code = $_SESSION['frequent_code'];}

if (zen_not_null($_POST['frequent_code'])) {$_SESSION['frequent_code'] = zen_db_prepare_input($_POST['frequent_code']);}
$frequent_code = $_SESSION['frequent_code']; 

ALSO I added the same code to includes/modules/pages/checkout_payment/header_php.php (but probably just need to add it to checkout_confirmation/header_php.php)

EDIT
includes/modules/pages/checkout_payment/header_php.php

ADD

if (isset($_SESSION['frequent_code'])) {$frequent_code = $_SESSION['frequent_code'];}

if (zen_not_null($_POST['frequent_code'])) {$_SESSION['frequent_code'] = zen_db_prepare_input($_POST['frequent_code']);}
$frequent_code = $_SESSION['frequent_code']; 

UNDER $_SESSION['comments'] = $_POST['comments'];