clear your browser cache, then close the browser completely and try again.
make sure you are processed through to the checkout success page that you added the code to before trying to create a new order.
keep in mind, power store has 2 success pages, checkout_success.php and pp_cehckout_success.php, the code will need to be on both pages.
also make sure the change is being uploaded to the server, sometimes when you make a code change, the file may not upload correctly and there is no way to see it. One trick I use is to add today's date to the body of the page, or some other visual change, if I cant see that change then I know it did not upload correctly.
