Carrier billing lets you buy apps, games, or services and charge them directly...

https://miloyyxi461.huicopper.com/how-do-i-decide-when-to-use-carrier-billing-vs-a-card

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