Carrier billing lets you buy digital content or services and charge the cost...

https://www.active-bookmarks.win/carrier-billing-lets-you-buy-apps-games-or-services-and-charge-the-cost

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