Carrier billing lets you pay for digital purchases by adding the cost to your...

https://www.apu-bookmarks.win/carrier-billing-lets-you-buy-apps-games-or-services-and-pay-through-your

Carrier billing lets you pay for digital purchases by adding the cost to your monthly phone bill or by using the credit you have on a pay-as-you-go plan. This method is easy to use since you don’t need a credit card or separate app