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

https://sergioxljg203.cavandoragh.org/what-can-i-buy-with-pay-by-phone-billing

Carrier billing lets you buy apps, games, or services 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 taken from your available credit