Carrier billing lets you pay for apps, games, or services by charging the cost...

https://www.pawn-bookmarks.win/carrier-billing-lets-you-buy-things-using-your-phone-instead-of-using-a-credit

Carrier billing lets you pay for apps, games, or services by charging the cost directly to your phone bill. If you have a monthly plan, the charge appears on your next bill. For pay-as-you-go users, the amount is taken from your available credit