Carrier billing lets you buy apps, games, or services and charge the cost...

https://ariassplendidinsight.swiftnestly.com/posts/why-does-carrier-billing-feel-faster-than-card-checkout

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