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

https://www.coast-bookmarks.win/carrier-billing-lets-you-pay-for-apps-games-or-services-by-adding-the-cost-to

Carrier billing lets you buy apps, games, or subscriptions and charge them 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 amount is subtracted from your available credit