Method and architecture for facilitating payment to e-commerce merchants via a payment service. The method enables consumer users of an electronic storefront hosted by a merchant to make purchases via the payment service, wherein interactions between the electronic storefront and the payment service are transparent to the user. In response to a user check-out request, the user's browser is directed to a payment service web site. Information from which authorization for use of the payment service may be determined is passed to the payment service. The payment service then returns the browser to a selected check-out flow hosted by the electronic storefront, wherein the check-out flow provides an option to use the payment service if the user and merchant are authorized to do so, otherwise the check-out flow does not include the payment service option. In one embodiment, an application program interface (API) provided by the payment service is employed by the electronic storefront to facilitate transactions with the payment service.