Carrier billing lets you buy digital products or services using your phone...

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

Carrier billing lets you buy digital products or services using your phone account. Instead of entering credit card details, your purchase cost is simply added to your monthly phone bill or taken from your prepaid balance if you have a pay-as-you-go plan