One call sell information, that would be commerce in information. But if you are managing someone else's information (or payments), that is providing a service.

"payment and information service" gets 375,000 google hits, "payment and information commerce" gets only your question here.

I think the phrase, with service, may be more common in the UK and the commonwealth, but here are a few examples including one selling in the US, and one from an American organization. If these examples fit what your client is selling, I think the examples themselves should be somewhat compelling.

"Electronic payment services provider VeriFone's US-based taxi business, VeriFone Transportation Systems (VTS) has teamed up with mobile operator Sprint to launch a wireless payment and information service for New York City taxis."
http://www.globalsmart.com/VeriFone Sprint launch pay

An early payment and payables information service that unlocks the financial supply chain for buyers and their suppliers
... payment and payables information service that unlocks the financial supply chain for buyers and their suppliers Enables buyers to improve their working capital and cost of procurement while providing their suppliers ...
30 Apr 2009 - URL: http://www.gresham-computing.com/resourcecentre/pdfs/CEarlyP...

In some respects vouchers resemble credit cards, although they are more specialized. In this regard (25), "A credit card-based payment and information service designed to streamline claims processing has been introduced on a limited basis by American Express Travel Related Services Co. Inc. American Express's new card, called Quattro, will be used by 500 of its workers and those of John Hancock Financial Services in the Boston area"(25).
http://clinicalfreedom.org/CLFREE01.HTM

THIS IS A DESCRIPTION OF ANOTHER SUCH SERVICE, WITHOUT USING THE EXACT PHRASE:

A complete solution from a single supplier Civica provides the leading integrated solution for income management, e-payments and cash receipting. Installed in over 175 local organisations, Civica ICON manages payments from all sources across all departments 24 hours a day. Electronic channels provide a highly efficient and convenient method of delivering services and responding to increased public expectation to pay bills using credit and debit cards. ICON provides a complete solution for tracking income from receipt to banking, reconciliation and dispersal of monies collected. Through modular internet, intranet, phone and kiosk payment channels, ICON helps housing providers realise the benefits of less labour intensive and cheaper processes, releasing scarce resources to front line services.

Online payment and transaction processing as part of the delivered service is imperative, either in a stand-alone environment or as an embedded process. Housing providers require a single corporate solution that provides a fully integrated approach to multi-channel income processing – a system that is powerful and flexible, easy to implement and above all robust and reliable. ICON is the only solution available that meets this challenge.

The advanced functionality of ICON also provides one of the major building blocks to enable more sophisticated transformation initiatives. Interactive citizen portals, CRM solutions and truly interactive websites employing intelligent forms can all be payment-enabled using the ICON Paylink modules.
http://www.civicaplc.com/UK/Sectors/Social Housing/Payment S...