A few days ago, we reported that the Play Store is beginning to offer a new payment option for users. Starting in Mexico, users can top up their balance at a convenience store, so they don't need to have a credit card, carrier billing, or any other payment method linked to their account. At I/O, Google officially introduced the feature and explained how it works.
Developers will be able to give their users a new option for a deferred payment, letting them purchase the app, then pay for it at a convenience store. They'll get a payment code on their screen that they need to show the cashier in order to complete the purchase, and in ten minutes, they should get a confirmation then be able to download and start using the app or game. It's called "Pending transactions" and it's currently available to users in Mexico and Japan.
You can see the brief moment this is mentioned in the Google I/O presentation below (queued to the exact time), and read more about it in the official documentation.