Carrier billing lets you pay for apps, games, or services by charging the cost...
https://www.sierrabookmarking.win/carrier-billing-lets-you-pay-for-purchases-using-your-phone-account-instead-of
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