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

https://sergionyxy407.tearosediner.net/why-did-my-carrier-billing-payment-get-declined

Carrier billing lets you buy apps, games, or content and charge the cost directly to your phone bill. You can either add it to your monthly invoice or have it taken from your prepaid credit if you use pay-as-you-go