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

https://web-wiki.win/index.php/Why_Does_Carrier_Billing_Feel_Faster_Than_Card_Checkout%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. For pay-as-you-go users, the amount is taken from your available credit