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

https://stephenczub458.theglensecret.com/what-is-direct-carrier-billing-and-how-is-it-different

Carrier billing lets you buy apps, games, or services and charge the cost directly to your phone. Instead of using a credit card, purchases appear on your monthly phone bill or are taken from your pay-as-you-go credit