Carrier billing lets you buy digital goods or services and charge the cost...

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

Carrier billing lets you buy digital goods or services and charge the cost directly to your phone bill. If you have a monthly plan, the purchase shows up on your next bill. With pay-as-you-go, the amount is taken from your available credit balance