Mobile Platform

On mobile platform's the built-in app selection/filtering mechanism can fulfill the role of the Payment Mediator.

The browser simply hosts the Payee interface and converts the paymentRequest into a form that can be used to invoke the platform's app selection flow.

The Payment App is simply a mobile app that registers itself with the platform via it's manifest, as being capable of processing payment requests and specifies the payment methods and terms it supports.

Note: Current app selection logic in mobile platforms does not have the filtering granularity that may be required to filter Payment Apps based upon complex payment terms.

In this deployment the mobile OS also fulfills the role of Payment App Host.