I need to figure out how to use the PayPal IPN thing. And for experimentation with PayPal things, you should of course not use live accounts. You could, but it’s probably not the best idea. Luckily, PayPal has something they call a Sandbox where you can create and manage fake PayPal accounts that you can experiment with.
It’s not very difficult to get started, but there was a couple of points that wasn’t totally clear to me at first. Therefore I thought I could document it here.