Unity don't process windows message(like a WM_KEYDOWN) when it run in background!

i want to send a WM_KEYDOWN windows message to Unity when it is running in background.

I have already done it. But Unity did not immediately processing. Unity process that message when it get focus.

I have already selected the “Run In Background” options.

That’s all. I don’t have to find useful information on Google.

I would appreciate it if you could help me. Thanks!

Did you ever figure this out? This is exactly my problem.