Carrier billing lets you pay for apps, games, or services by adding the cost to...

https://melissazxlth.gumroad.com/p/how-do-i-pay-with-carrier-billing-on-a-monthly-plan

Carrier billing lets you pay for apps, games, or services by adding the cost to your monthly phone bill or subtracting it from your prepaid credit. It’s a simple way to make purchases without using a credit card