A+ Sync with GCal. How to get private key


Im trying to setup sync GCAL with a appointment+, but it keeps saying that the private key doesn't exist. My private key is named "Book-7410b9312909" as standard, so I think I am doing something wrong. I followed the guide the Gcal page in appointment+ settings, but that guide is really old and the developer console has changed a lot since then. It is supposed to to sync both ways..

Can you please help with a couple of steps to get the correct GCal privat key?