I found it:
Extra steps for Cordova
Google Play Game Services are designed to work in a web browser, but it's possible to also configure it to work in Cordova (e.g. when exporting to mobile via PhoneGap Build or the Intel XDK). To set it up for Cordova you'll also need to:
Fill in the Client secret property with the value from the Google Play Developer Console.
Add http://localhost as one of the redirect URIs in the API console.
Remove any uses of On auto-sign in failed. It never triggers in this mode, so you will need to rely on having manual sign-in instead.
Client secret property? Redirect URI API console? I do get Auto-sign in fail, but i dont get the client secret property or redirect URI API, sorry. I have no idea where to find the Client secret property or redirect URI API.
I found the Client ID thing. Where in Construct 2 do I put it? I found the Client ID, but it says view Client Secret ID in API Manager, I clicked but there is no Client Secret ID in the API Manager.