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

https://www.bright-bookmarks.win/carrier-billing-lets-you-buy-apps-games-or-services-and-have-the-cost-added

Carrier billing lets you buy apps, games, or subscriptions and pay for them through your phone account. Instead of using a credit card, the cost is added to your monthly phone bill or taken from your prepaid credit if you have a pay-as-you-go plan