Add In-App Purchases to existing iOS Application

I want to add in-app purchases to my existing iOS app ([login to view URL]). I built the app but can't figure out in-app purchases and don't have tons of time to keep trying myself. I'm looking for someone who has implemented in-app purchases before and can work with Objective-C and iTunes Connect to get the two working together. If you've done this before it should be a very quick project. My goal is to add paid levels to my app with the ability to add more on-the-fly without users having to update the app. * Written in Objective-C * Code should be commented * Should be able to add additional in-app purchases on-the-fly