Thanks to a server-side update, iOS users in a number of countries can now use Apple Pay to pay for digital purchases from Apple, including iTunes, the App Store, iCloud storage, or an Apple Music subscription.
According to Apple's support page for Apple ID payments, the change is live in the United States, Canada, Russia, Ukraine, Australia, Singapore, Taiwan, Hong Kong, and United Arab Emirates.
If you open your Settings app, tap on your Apple ID at the very top, then tap Payment & Shipping, you'll see a list of possible payment methods. Here in the United States, that has always included most major credit cards, PayPal, or a balance added to your Apple ID through gift cards and the like. Tap Add Payment Method to add a new one: you'll see a Found in Wallet section showing cards you can add, including Apple Pay Cash here in the U.S.
