HID Device for Android Car Navigation

I just made an interface that controls the volume of a device connected thru USB. Tested it on my PC and on a Samsung Note 8. It is working fine. When i connect it to the navigation, nothing. I have installed a serial usb app and it receives the codes. It doesn't know what to do with that codes. The navigation is running android 7.1.

What does this "interface" consist of? An Atmega microcontroller? Some other brand? What software does it use, your own? or a copied one?

Arduino Mega ADK and i changed the firmware so i can use HID library ( hoodloader 1.8 ) .