Carrier billing lets you buy apps, music, or services and charge them directly...

https://riversinspiringblogs.evergrovio.com/posts/does-carrier-billing-work-if-i-switch-to-a-new-phone

Carrier billing lets you buy apps, music, or services and charge them directly to your phone bill. If you have a monthly plan, the purchase shows up on your next bill. For pay-as-you-go users, the cost is taken from your available credit