This plugin was setup with Google Calendar API integration in January of 2015. It was working great but somehow with a recent update it no longer would update or send data to the Google calendar. (The calendar on the website side was working fine just not updated the Google calendar automatically). It appears the website lost those settings under the Google Settings tab. So we deleted the existing Calendar API credentials in Google and started fresh. We got as far as entering the client id and secret code. We then generated the access code and submitted on the site but once entered we receive this error Authentication failed: Error fetching OAuth2 access token, message: 'invalid_client'