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

https://bizzmarkblog.com/carrier-billing-for-subscriptions-is-it-easy-to-cancel/

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