Carrier billing lets you pay for apps, games, or subscriptions by charging the...

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

Carrier billing lets you pay for apps, games, or subscriptions by charging the amount directly to your phone bill. If you have a monthly plan, the cost appears on your next bill. For pay-as-you-go users, the purchase is deducted from your available credit