For more current information, see https://rsvpmaker.com/blog/category/paypal/
This tutorial shows how to integrate PayPal with RSVPMaker so you can collect a fee for admission or other fees associated with an event.
The PayPal configuration seems to be the part of RSVPMaker setup people have the most trouble with, and the directions are a little tricky. I hope this will help.
Because there’s money involved, I’ve tried to be careful to make this as secure as I know how, following the guidelines from PayPal. That’s the reason I make you jump through a few extra hoops, creating a file in a secure location on the server to contain the PayPal parameters, rather than simply providing a configuration screen in WordPress. You don’t want someone using the API access to get into your PayPal account (and potentially your bank account), so it’s worth taking a little more time to do it right.