Custom action in Ribbon.PublishTab always disabled

I have a custom action which I want to place at the PUBLISH tab of the page. To do so, I have a following code for custom action.

<CustomAction Id="D7D4B708-783C-4221-8798-6A465C614B57.StartWfsEditMode"
            Location="CommandUI.Ribbon"
            Title="Start"               
            Sequence="10005">
<CommandUIExtension>
  <CommandUIDefinitions>
    <CommandUIDefinition Location="Ribbon.PublishTab.Workflow.Controls._children">
      <Button Id="Lofbergs.DocsStartWFEditMode"
              Image16by16="/_layouts/15//Images/Approval_16_by_16.jpg"
              Image32by32="/_layouts/15//Images/Approval_32_by_32.jpg"                     
              LabelText="Start Workflow"                 
              Sequence="2"
              Command="StartWorkflow1"
              TemplateAlias="o1"/>
    </CommandUIDefinition>
  </CommandUIDefinitions>
  <CommandUIHandlers>       
    <CommandUIHandler Command="StartWorkflow1" CommandAction="javascript:function StartWorkflowEdit()
                      {
                        alert('hello');
                      }
                      StartWorkflowEdit();">
    </CommandUIHandler>
  </CommandUIHandlers>
</CommandUIExtension>
</CustomAction>

The custom action is getting displayed on the tab but it is always disabled for selection.

What am I missing in my code?