1. A system, comprising: a communication interface configured to communicate over a network with a payer and a payee; a transaction handler configured to process transactions between issuers and acquirers in response to account identifiers of customers, as issued by the issuers, being submitted by the acquirers, the acquirers to receive payments on behalf of the merchants and the issuers to make the payments on behalf of the customers; and a web service apparatus coupled with the transaction handler, the web service apparatus configured to: generate a unique identifier for a payment by the payer to the payee; send, via a payment service accessed by the payer using a user interface on a client device, the unique identifier to the payer; receive, from the payee, the unique identifier and information about a first account of the payee into which payments are to be received, the first account issued by a first issuer, wherein the payee has previously received the unique identifier via an alternative communication channel other than the payment service; communicate the information about the first account to the transaction handler; receive, via the communication interface, an invoice from the payee; receive, via the communication interface, layout information from the payee to configure the invoice; configure the invoice for presentation to the payer based at least partially on the layout information; present, via the communication interface, the invoice to the payer, the payer having a second account issued by a second issuer, the presenting to cause display of the invoice in the user interface of the client device and to present, in the user interface, a link associated with the invoice; receive, via the communication interface, a payment request initiated by the payer via the user interface using the link; and in response to the payment request, electronically communicate, using the transaction handler, with computing devices of the first issuer and the second issuer, the electronic communication to cause the computing devices to charge the second account of the payer and credit the first account of the payee according to the invoice.