Carrier billing lets you buy apps, games, or services and have the cost added...

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

Carrier billing lets you buy apps, games, or services and have the cost added directly to your monthly phone bill or taken from your pay-as-you-go credit. It’s a simple way to pay without needing a credit card or separate account