Carrier billing lets you buy digital goods 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 digital goods or services and charge the cost directly to your phone bill. If you have a monthly plan, the purchase shows up on your next bill. With pay-as-you-go, the amount is taken from your available credit balance