There was no endpoint listening at domain.com/.../PagesApprovalWorkflow.xamlx that could accept the message. This is often caused by an incorrect address or SOAP action. See InnerException, if present, for more details.
The WorkflowBaseURL needs to be set to the domain of the website for example, http://mydomain.com The property can be found under Administration -> Settings -> Advanced -> System -> ServicePaths.
You might also need to add your domain and its INTERNAL IP to the Server’s Hosts File.