Why In-App purchase sandbox always ask “Verification Required”?

Question

I have signed out from the store in device settings. I entered user credentials only in my App. I have set up a brand new (actually around 4 times) test user.

Why th

Answer 1

If you are having such problem for 4th IAP item to buy.

It looks, each test account does not work for purchasing more than 3 items of an application. You may create a new test account from itunesconnect.apple.com->Manage Users->Test User to test your 4th IAP item.