How to FIX Bluetooth connection/pairing problem of Android Head Unit

Video addresses to Bluetooth pairing issue between Android Head unit and other devices.
I apologize for my poor English.
In my case, when I purchased and installed the head unit first, couldn't manage to pair head unit with my OBD2 adapter. I was almost giving up to find solution to this until the steps I followed in this video.
PIN CODE that worked in car settings section: 000000