JSOM : run work flow using Javascript

I am trying to run a workflow using JSOM for office365 workflow

I have used this cod to call the function :

<a href="javascript:startWorkflow(\'{FF71E26B-04B8-42CF-B641-30819F122C25}\', '19')">Request for update</a></li>

and for the java script :

function startWorkflow(itemID, subID) {

                        var context = SP.ClientContext.get_current();
                        var web = context.get_web();

                        var wfServiceManager = SP.WorkflowServices.WorkflowServicesManager.newObject(context, web);

                        var subscription = wfServiceManager.getWorkflowSubscriptionService().getSubscription(subID);

                        context.load(subscription);

                        context.executeQueryAsync(
                            function (sender, args) {
                                console.log("Subscription load success. Attempting to start workflow.");
                                //notify_i('Request failed', 'Subscription load success. Attempting to start workflow.' + '\n' + args.get_stackTrace());
                                var inputParameters = {};

                                wfServiceManager.getWorkflowInstanceService().startWorkflowOnListItem(subscription, itemID, inputParameters);

                                context.executeQueryAsync(
                                    function (sender, args) { console.log("Successfully starting workflow."); },
                                    function (sender, args) {
                                        console.log("Failed to start workflow.");
                                        console.log("Error: " + args.get_message() + "\n" + args.get_stackTrace());
                                    }
                                );
                            },
                            function (sender, args) {
                                console.log("Failed to load subscription.");
                                console.log("Error: " + args.get_message() + "\n" + args.get_stackTrace());
                            }
                        );
                    }

I am getting this error message:

Subscription load success. Attempting to start workflow. OpenSubjects.aspx:806 Failed to start workflow. OpenSubjects.aspx:807 Error: Value cannot be null. Parameter name: subscription undefined