Carrier billing lets you buy apps, music, or services and charge them directly...

https://blast-wiki.win/index.php/How_Do_I_Check_for_Unexpected_Charges_on_My_Phone_Bill%3F

Carrier billing lets you buy apps, music, or services and charge them directly to your phone bill. If you have a monthly plan, the purchase shows up on your next bill. For pay-as-you-go users, the cost is taken from your available credit