Carrier billing lets you buy things like apps or music and charge the cost to...

https://www.kilobookmarks.win/carrier-billing-lets-you-pay-for-apps-games-or-digital-content-by-adding-the-2

Carrier billing lets you buy things like apps or music and charge the cost to your phone account. Instead of using a credit card, the amount is added to your monthly bill or taken from your prepaid credit if you have a pay-as-you-go plan