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

https://www.bookmarking-fox.win/carrier-billing-lets-you-buy-digital-products-or-services-using-your-phone

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