Carrier billing lets you buy apps, games, or services and charge the cost...

https://www.bookmarkingqueen.win/carrier-billing-lets-you-buy-things-online-or-in-apps-and-pay-for-them-through

Carrier billing lets you buy apps, games, or services and charge the cost directly to your phone bill. If you’re on a monthly plan, the purchase will show up in your next bill. For pay-as-you-go users, the amount is taken from your available credit