Add simple coin store feature in ios app

Integrate (still today) a very simple coin store functionality to my ios app. The user will tap a button and a coin-store window should show up (I have already designed the .xib file for that) and user will be able to purchase 4 types of coin packs (I will configure by myself the IAP on itunes). Then after the user purchased, the coins will be transformed into credits to play the game. That's it! Nothing more. The game is the following: [login to view URL]