queryFreeBusy returns provider busy intervals without exposing event details.
Use it to check scheduling conflicts across people, rooms, or Google Groups.
Example
Inputs
calendars is a required array of 1–50 exact calendar titles, IDs, or Google
Group IDs. RFC 3339 timeMin and timeMax are required and the end must follow
the start. timeZone optionally controls the response timezone; account
selects the Google account.
Output
errors; Google can return partial results when a calendar is inaccessible or
a group cannot be expanded.