I am trying to follow the instructions from this thread: https://www.zen-cart.com/showthread....-Donate-Button
I must say this is exactly what I want for my page. Unfortunately when I copy adn paste the code in to the product info display template the page with the product ID I put there is not showing . I already backup the with the old file version. Can somebody help me with this? Also I would like to set the entire category as donation products. So called Pay what you want. Is it then possible by changing the code? Instead of

($_GET['products_id'] == 500) {to ($_GET['categories_id'] == 500) { ???
Also where exactly should I copy this? Which line?