Back in October 2018, Google announced that they would be sunsetting Consumer Google+ in August 2019. Two months later Google announced that they would be accelerating the shutdown of Google+ for consumers to April 2019.
Google+ API shutdown has accelerated to March 7, 2019. As this is a progressive shutdown, calls to these APIs will start to fail as early as January 28, 2019, intermittently. As our users may begin to experience these issues earlier, we will be removing Google+ from February 15, 2019.
We will try to make this experience as smooth as possible and should you be experiencing issues posting to Google+ through Sendible this could be because of the depreciation.
In case you were wondering, the depreciation of Google+ won't have any effect on Google My Business.