GCal & Google Business Apps not working

I get this error in my log. I am trying to synch Appointments Plus with my Business apps GCal account. I see activity in the business console and I spoke to Google and they said my account is fully enabled for API usage.

Insert went wrong: Error calling POST https://www.googleapis.com/calendar/v3/calendars/rhgfx.com_tr84s6cgtra9j2gv57ookc25qo%40group.calendar.google.com/events: (403) Forbidden

Please advise. Thank you