You are not doing anything wrong, the problem is that the page in the code is specified with a lowercase 'p'. The actually page name has a capital 'P', so the fix is to update the coupon_insert page so that it goes to the page with the correct name. The line of code this is set on is 41 on the coupons_insert.php page. I'm including an updated copy of the page for you so that you don't have to get into the code yourself.