Carrier billing lets you buy apps, games, or subscriptions and charge them...

https://wiki-zine.win/index.php/How_Do_I_Know_If_My_Mobile_Operator_Supports_Carrier_Billing%3F

Carrier billing lets you buy apps, games, or subscriptions and charge them directly to your phone bill. If you have a monthly plan, the cost appears on your next bill. For pay-as-you-go users, the amount is subtracted from your available credit