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

https://tango-wiki.win/index.php/Can_I_Buy_Transport_Tickets_with_Pay_by_Phone%3F

Carrier billing lets you buy apps, games, or subscriptions and charge the cost directly to your mobile phone account. The amount can either be added to your monthly phone bill or deducted from your pay-as-you-go balance