It seems that Apple has once again moved the Redeem button. The Redeem feature allows the ability to use promo codes to redeem applications from the App Store.
The Redeem option has now been moved to into the App Store application under the Featured option. Once in the Featured option, you will need to go into the New category and scroll all the way to the bottom… there you will see Redeem.
The button was previously located in the iTunes application under the More option. Before that, it was located (just for a short time) in the App Store application under a More option (the More option no longer exists). And before that, it was located in the iTunes application in the Downloads option (before there was a More option in iTunes). It seems Apple cannot seem to make up it’s mind on where this feature fits in. Personally, I think the new place they have chosen it a little awkward, but maybe I will get used to it.