Why can’t I make in app purchases?

Please read again -> Related Article -> If your payment method is declined in the App Store or iTunes Store

• If you still need help, contact Apple Support.

In-app purchase failed, even though there is more than sufficient “store credit” on the account. I am (still) able to purchase books and music with store credit, but in-app fails and subscription purchase may have failed.

Contact Apple Support -> Get Support (apple.com)