after this step https://developers.google.com/games/services/console/enabling#b_create_a_client_id i have a invalid sertificate error. what is the solution
Happens to me once when I use early version of buildbox. I try to update my game with higher version of buildbox and I got this certifacte problem. My solution is I unpublish my apps from android and re-upload with the different name/SKU/package name. but this is not helping if your apps already have millions download....
Not sure if this is your issue... but on Google Play you 100% have to use the same certificate for all updates of the same game. If you did not save your certificate (or forget the password) then you do need to create a new bundle ID and create a new instance of the game. There is no way to recover a lost certificate or forgotten password if you don't remember it.