buy-find-npo-part-2.php:
form uses get method:
<form id="NewNPOForm" name="NewNPOForm" method="get" action="purchase-coupon-book.php">
validation trigger uses post:
if (isset($_POST["ChooseNewNPObutton"]) || isset($_POST["ChooseNewNPObutton_x"])) {
change to get:
if (isset($_GET["ChooseNewNPObutton"]) || isset($_GET["ChooseNewNPObutton_x"])) {
same on the other page, form uses get method, trigger uses post.