I need one of my in-app purchases to be free, possibly with the provided by Apple IAP structure?
Currently the type of that purchase is non-consumable while it's payed everything is okay, but the problem is that if i made it 'free" from price tiers, i receive it's ID in invalidProductIdentifiers.
NOTE This was accurate when it was written, but has since become outdated
You cannot have a free In App Purchase. Think about it. What would Apple gain by giving you free hosting for your stuff? If you charge for it they get 30% and that makes them happy but 30% of nothing is nothing. You will need to host the content yourself.
Source: My experience with IAP