I had already made sure that the Settings for Incoming calls had the "Force background" and "Wi-Fi keep alive" were enabled.
These settings allow the app to stay alive in the background and this IS working because the app does actually wake up on an incoming UDP packet and seems to even put a notification on the lock screen about the incoming call, its just that you are not aware of it because it fails to wake up the phone (screen stays black) and there is no sound.
So its working in the background, just need it to wake up lock screen and play raining sound as the other apps (Bria & Groundwire) do.
Look forward to more help