Carrier billing lets you buy apps, games, or services and pay for them through...

https://wiki-fusion.win/index.php/Why_Do_Mobile_Operators_Put_Spending_Limits_on_Carrier_Billing%3F

Carrier billing lets you buy apps, games, or services and pay for them through your mobile phone account. Instead of using a credit card, the cost is added to your monthly phone bill or taken from your prepaid balance