How to buy coin?

When I try to buy coin, there is a pop up says that I need to contact iTunes support to complete this transaction. Any1 know how to solve it?

[support9]

please kindly contact iTunes support to confirm what kind of problem occured in the midst of your purchase and see what do they suggest.
Any support or assistance from our side, please feel free to letter kingdomsupport@haypi.com or any in-game support.

[DemonB3]

I am Having trouble Purchasig coins from the game. I use iTunes and I have money on my account But it says I have insufficient store credits remaining? Can anyone Help me solve this problem?
-DemonB3