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

https://dibz.me/blog/why-do-carriers-cap-carrier-billing-daily-or-monthly-1245

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