This will be a progressive shutdown, with intermittent failures starting as early as January 28, 2019.
Google+ API Shutdown
On March 7, 2019, all Google+ APIs will be shut down. This will be a
progressive shutdown beginning in late January, with calls to these APIs
starting to intermittently fail as early as January 28, 2019.
Developers should have received one or more emails listing recently used
Google+ API methods and Google+ OAuth scope requests in their projects. Whether
or not an email was received, we strongly encourage developers to search for
and remove any dependencies on Google+ APIs from their applications.
The most commonly used APIs that are being shut down include:
Beginning March 7, all OAuth token requests with scopes starting with "plus."
(i.e. "plus.me", "plus.login", "plus.profile.emails.read", etc) will fail
upon request, and may start to intermittently fail as early as
February 15, 2019.
The Google+ Sign-in feature has been fully deprecated and
will also be shut down on March 7, 2019. Developers should migrate to the
more comprehensive Google Sign-in authentication system.