The game was created with Corona SDK Starter which is free. Google Play Game Services is already implemented in the game's code and on Google Play, but there is a bug somewhere, because the game doesn't connect properly: when I open the game, I see "connecting to Google...", then a white ring and that's all, never a "welcome xx ..." message that I get with another game I have. And the game's button to see Google Play leaderboards doesn't open anything.
So all the coding is already done, the iOS version working fine, you only need to find and fix the bug on Android.
This project is finished when the game connects properly with Google Play Game Services, scores are sent to the leaderboards and the game's "scores" button works opening Google's leaderboards.