Okay, I completed the "all app" section by adding my game, I'm waiting for the alpha to be published right now. The play service is also linked to the app with the "com.myname.mygame" url.
Sorry about the code, I just followed the manual about Google Play plugin. Google play is supposed to launch at the start of the game, then if it has automaticaly sign in the player, it goes to the menu (layout start), and if it fails, it show a login window (set with buttonclick =1) and the player should be able to log in thanks to the button.
I don't know if the code is correct or not, and if it was not working cause I didn't add my game to the "all applications" section. Now, I should wait for the alpha to be published before testing it again right ? If yes, were am I supposed to go to test it again ? Should I just import the apk I put in the google play console on my phone ?