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

https://wiki-planet.win/index.php/How_Do_I_Pay_With_Carrier_Billing_on_a_Monthly_Plan%3F

Carrier billing lets you buy apps, games, or services and charge the cost directly to your phone bill. If you’re on a monthly plan, the purchase will show up in your next bill. For pay-as-you-go users, the amount is taken from your available credit