Developing for Dynamics GP and Inside Microsoft Dynamics GP have coverage of new Online Services for Microsoft Dynamics GP. New online Payment and Commerce services will be available to customer current on their enhancement plan starting November 1. Customers will need to be on GP 2010 SP1 or GP 10 SP5. Here is Inside Microsoft Dynamics GP post with more details.
Online Services for Microsoft Dynamics GP
Off-Topic & MiscellaneousGP 2010GP 10
Archived post from 2010. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.