Suddenly unable to make in-app purchases

I'm trying to make an in-app purchase in a game, it worked last week without any errors but now all of a sudden i'm unable to purchase anything. I have $150 credit on my iTunes but whenever i try making a purchase it says "You Purchase Could Not Be Completed; For assistance contact iTunes Support"

The support page does not help me in any way. I've tried signing out on both the game and iTunes, restart my phone many times and checked my date/time settings but nothing works.

Need some extra help here.