If the coding is correct sounds like the mic is open circuit. So its either a bad connection, not connected, broken wire, broken mic ir plugged into the wrong socket.
As fot LED tail lights
https://youtu.be/9RPHg3cZGugFast forward to 7:28 and he shows you how to manually change byte 18.
For uk cars 15 is the setting for byte 18 and is the setting recomended by staff at VCDS.
Some very very early 2009 cars iirc don't have the software version to allow bypass the warning, fingers crossed yours isn't one of them.