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

https://charlieeocd131.lucialpiazzale.com/why-do-mobile-operators-put-spending-limits-on-carrier-billing

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