Iphone in-app purchases needs verification? How to fix?

On my iphone 5, i'm trying to buy the $5 pile of gems in Clash Of Clans however, I DO HAVE ENOUGH. 15 in my account but when ever it says "Confirm in-app purchase?" I click buy (This is usual, I bought the same thing for the same game a while back) then I type my Itunes password but right then instead of buying the gems, another message pops up saying "Verification required" which it says I have to do. When I click continue, it takes me to the app store trying to make me select a payment type and the "Itunes balance" button or whatever isn't there! What do I do to make the "Confirm" message stop poping up and just charge my balance?!

Yehh