Having sub-menu is absolutely valid case. The only problem I see is that you added insertBefore="payment" for sub-menu, but it’s impossible to insert sub-menu before its parent. Also, I’d recommend adding id for sub-menu.
Thankyou Gelb! It worked.
But I see different prob now.
Under payment ,my sub menu is payment settings. But I can see the caption is “menu.config:Payment Settings”