Not able to purchase the gold

I have a problem in purchasing the gold through app purchases.i am not able to select small crate of gold,medium crate of gold,large crate of gold..Please rectify the issue or help me out in doing this purchase.i dont have any problem with my apple account in doing the purchases.i am able to buy other APPS.i do have problem only with this game.

Srivejandla about Frontline Commando