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

https://brookssnewinsight.scriblorax.com/posts/what-is-the-gsma-open-gateway-for-carrier-billing

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