Carrier billing lets you buy apps, games, or subscriptions and charge the cost...

https://miloyyxi461.huicopper.com/carrier-billing-stopped-working-after-i-changed-my-plan-what-you-need-to-know

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