Source: Google+ APIs shutting down March 7, 2019 from Google Developer
As part of the sunset of Google+ for consumers, we will be shutting down all Google+ APIs on March 7, 2019. This will be a progressive shutdown beginning in late January, so we are advising all developers reliant on the Google+ APIs that calls to those APIs may start to intermittently fail as early as January 28, 2019.
On or around December 20, 2018, affected developers should also receive an email listing recently used Google+ API methods in their projects. Whether or not an email is 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:
As part of these changes:
While we’re sunsetting Google+ for consumers, we’re investing in Google+ for enterprise organizations. They can expect a new look and new features — more information is available in our blog post.