There are instructions included inside the plugin for setting up the link with the Google Calendar API.
Those instructions appear to be outdated, and following them basically does not work any more.
The biggest issue appears to be that it no loner allows you to pick a "Service account" (step 8) and instead it offers Web application and a few others.
Then, it doesn't have a download option (step 10). So, I don't know what to do.
Can you help?