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

https://www.kilobookmarks.win/carrier-billing-lets-you-pay-for-apps-games-or-digital-content-using-your

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