Carrier billing lets you buy apps, games, or services and charge them straight...

https://cashsexcellentblogs.rivetgarden.com/posts/carrier-billing-for-subscriptions-is-it-easy-to-cancel

Carrier billing lets you buy apps, games, or services and charge them straight to your phone bill. Whether you have a monthly plan or use pay-as-you-go credit, the cost is added to your next phone bill or deducted from your available balance