Carrier billing lets you buy apps, games, or digital content and charge the...

https://blogfreely.net/neasalnfbo/are-carrier-billing-limits-a-feature-or-a-bug

Carrier billing lets you buy apps, games, or digital content and charge the cost directly to your phone account. If you have a monthly plan, the purchase appears on your phone bill. With pay-as-you-go, the amount is taken from your available credit