I was notified that the PayPal links on the Tipping page did not work. I think the problem was related to something Drupal (the content management system on this site) does to the code I pasted from PayPal. When I changed to a content type where Drupal does no transformations, it started working.

Thanks to the kind individual who notified me about this. And of course, thanks for the tip! (And feedback, glad you liked the book.)