Google Play Games Services is a service that helps developers with building games that are fully feature on the online side, like achievements, leaderboards, and more. Unfortunately, not all of those features are being used.
Google has announced that Gifts, Requests, and Quests were not being used as much as other features and thus are being removed on March 31, 2018. Though there will be no support starting now, but developers will be able to use the features for another year.
The latest SDK also cut out support for iOS, and support and updates for the iOS SDK are no more. Usage of GPGS on iOS was very low so Google didn’t find it worth supporting any longer.