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

https://wiki-canyon.win/index.php/Can_I_Use_Carrier_Billing_for_App_Store_Purchases%3F

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. On pay-as-you-go plans, the amount is deducted from your available credit