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

https://ariassplendidinsight.swiftnestly.com/posts/how-do-i-pay-with-carrier-billing-on-a-monthly-plan

Carrier billing lets you buy apps, games, or services and charge the cost directly to your monthly phone bill. If you use a prepaid plan, the amount is taken from your available pay-as-you-go credit