Carrier billing lets you buy apps, games, or subscriptions and charge them to...

https://mighty-wiki.win/index.php/Carrier_Billing_vs_Digital_Wallets:_What_Is_the_Difference%3F

Carrier billing lets you buy apps, games, or subscriptions and charge them to your phone bill. If you have a monthly plan, the cost appears on your next bill. For pay-as-you-go users, the amount is taken from your available credit