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

https://milosimpressivejournals.quillnesty.com/posts/what-is-direct-carrier-billing-and-how-is-it-different

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