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 bill. If you have a monthly plan, the purchase adds to your next bill. With pay-as-you-go, the amount is taken from your available credit