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

https://mill-wiki.win/index.php/What_Is_Direct_Carrier_Billing_and_How_Is_It_Different%3F

Carrier billing lets you buy apps, games, or digital content 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 available credit