Google Play login is required

Need help guys :( When i tap "Enter Coupon" i receive this message "Game Center: Google Play login is required" but ive got my google login already but still experiencing :(

OS: android

I really need help guys :(

Why it would say Google play log in Is required. My thought it Is log in automatically while the app Is open. Pls fixed the problem fast. We really Love the game.

When I tried to pvp battle it says:"Google play login required" Please fix it fast. I want to play pvp battle

Please help!

OS:Android