Why i can't add features on my feature service in flex

Hi. I have feature service published in ArcGIS server 10.2.1 but I can't add feature using flex. When I add new feature, the edit widget saying it's adding feature but after a while the geometry doesn't display or basically there is no new feature added to the data. When I tried to edit the sde feature in arcmap, it's all fine. What's wrong with my feature service?