Carrier billing lets you buy digital products or services and pay using your...

https://miloyyxi461.huicopper.com/carrier-billing-stopped-working-after-i-changed-my-plan-what-you-need-to-know

Carrier billing lets you buy digital products or services and pay using your phone account. Instead of a credit card, charges appear on your monthly phone bill or come out of your pay-as-you-go balance