As of version 5.5.5, WorkflowGen supports WCF Services with WebHttpBinding (HTTP POST requests).
The workflow application must use
application/xml; charset=UTF-8 encoding .
Click here to download an example of a WCF service project configured with WebHttpBinding.
For WCF Services using the SOAP protocol, refer to the Workflow Application: How to use a WCF Service as a workflow application with basicHttpBinding or wsHttpBinding FAQ.