Carrier billing lets you buy apps, music, or services and charge them directly...

https://www.bookmark-help.win/carrier-billing-lets-you-pay-for-apps-games-or-services-by-adding-the-cost

Carrier billing lets you buy apps, music, or services and charge them directly to your phone bill. If you have a monthly plan, the purchase shows up on your next bill. For pay-as-you-go users, the cost is taken from your available credit