I'd like to share from my experience and may be it would be a useful addition to your tutorial:
1. The application's bundle identifier should match the App ID we've created in the developer portal. Say you've create the following App ID: HD5583.com.yourCompany.YourApplication.
In Xcode project the bundle identifier should be com.yourCompany.YourApplication. Without the HD5583 prefix. It's very important. In iTunes when you mention bundle id, it also should say com.yourCompany.YourApplication.
2. Now another very important thing: Mobile provisioning profile. We need to create a new mobile provisioning profile for App ID we've created to sign with it the application.
3. ProductID in your sources. In the example you define the productID as "com.yourcompany.featureA". When preparing array of products, you need to state only "featureA" as product identifier. Other string combinations will result invalid product identifiers.

These are things I would need to figure out by myself. Hopefully somebody will benefit from this as I did from your great tutorial and answer.

So basically you say, that i should leave it as is or point the user to try again? The original alert from AppStore doesn't let user know what he should do next? I mean saying try again and so on...
How to handle it logically?

Thanks a lot!

But why it fails the transaction after the login and how i prevent it? My biggest concern, that it will happen to the user... Anyway to test I need to sign out the AppSore settings on the device, so it's like i'm changing the store... How do i catch/prevent it?

Thanks a lot for your help!

Hi,

Thanks for saving us hours of coding! works like a charm. But one strange thing is happening when i try to test the in app purchase:

I created a test user account through the Manage User Accounts in iTunes Connect. When you create such an account you have to select a valid storefront for your account. I chose US Store. Now I signed out from the store in App Store settings on my device. Ran the application and tried to perform a purchase. I successfully login with my test account. After I press Confirm when entering my credentials I get an alert, that comes from SKPaymentTransactionStateFailed from the observer. It says "Your account is only valid for purchases in the US iTunes Store". The error state = 0 unknown. Second time when i try to perform the purchase, StoreKit only asks me for a password like the previous login was successful. After entering a password I can perform a purchase. My question is whether it's only because it's a testing account and the application is not actually on AppStore? What should I do to avoid this message or at least to continue the purchasing process?

Any help is appreciated and again thanks for the great post!
Nava