Hi Raymond,
The reason behind not showing up approve/reject buttons is because of this : 'When you click on any link in work-inbox, it is not capturing correct workitem id. Try to pass work-item ID mauallly to the URL and check.It will show both approve and reject buttons.
For example : I tried to open the following URL having WORKITEM_ID of the request.It shows me required buttons as shown below
When i remove WORKITEM_ID parameter, it show no buttons on my approve screen.
Hope this helps you to resolve your issue.
Thanks
KH