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

https://www.last-bookmarks.win/carrier-billing-lets-you-pay-for-apps-music-or-other-digital-purchases-using

Carrier billing lets you buy apps, games, or services and charge the cost directly to your phone bill. If you have a monthly plan, the purchase appears on your next bill. For pay-as-you-go users, the amount is taken from your prepaid balance