Key event from other application from SDL application


I am working on image scrolling using SDL application. Its works fine.
Based on SDL_DOWN key event when i press “S” key image scrolling started in SDL window. I would like to pass/send the key event from my C# application to start /invoke the scrolling in SDL window , i tried with SendKeys.SendWait(“S”); based on google search but it did not work.

Does any special key event in SDL why its not working when i send key event to SDL window.

Looking forward your reply. Many Thanks.