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 appears on your next statement. For pay-as-you-go users, the amount is deducted from your available credit