Carrier billing lets you pay for apps, games, or digital content by charging...

https://rileysexcellentnews.readspirex.com/posts/is-pay-by-phone-billing-the-same-as-a-mobile-wallet

Carrier billing lets you pay for apps, games, or digital content by charging the cost to your phone bill. If you have a monthly plan, the amount appears on your next bill. For pay-as-you-go users, the charge is taken from your available credit