rsvpBOOK has 2 versions of the Admin Dashboard.  Which one do you have?

This screen prompts you for 3 values:

1. Email Address - this is the email address of the PayPal account owner
2. Identity Token - this is a string of characters that PayPal provides to you during your set up of your account
3. Certificate ID - this is a string of characters that confirms a secure connection between the PayPal server and rsvpBOOK's servers
4. Your final step, in order to confirm your PayPal connection, is to make a $1 test purchase - since you're the account owner, you can refund yourself the $1

See this article: How do I copy my PayPal settings to another event?