I just found that while the shared calendars can’t be viewed and thus not edited…Where read/write access to the shared calendar applies, calendar events can be created in the shared calendar on the phone and are shown in the Zimbra web based calendar after sync completes.
Google Base URL (April 2019)
Synchronization with Google CalDAV/CardDAV is not officially supported by Google or DAVx⁵. For some people it seems to work, for others it doesn’t. Google officially requires OAuth 2, which is not supported by DAVx⁵.
We have received updated information about Google CalDAV:
The old endpoint https://www.google.com/calendar/dav is deprecated and no longer supported.
Now you shout suggest https://apidata.googleusercontent.com/caldav/v2/calid/events
Please have a look on https://developers.google.com/calendar/caldav/v2/guide
Google Account security:
- If you use 2-Step-Verification for your Google account (recommended): Create an app password for DAVx⁵ and use the app password for signing in with DAVx⁵.
- If you’re not using 2-Step-Verification: To allow Basic auth clients like DAVx⁵ to connect, you need to “Allow less secure apps” in your Google account before setting up DAVx⁵.
If you have further information, please just post here.