Carrier billing lets you buy apps, games, or digital content and have the cost...

https://wiki-room.win/index.php/How_Can_I_Keep_Carrier_Billing_From_Messing_Up_My_Budget%3F

Carrier billing lets you buy apps, games, or digital content and have the cost added directly to your monthly phone bill or subtracted from your prepaid balance. It’s a simple way to pay without needing a credit card or separate account