Ninebot Max Error Code 27
"Control Board Password Error, Please replace the Control Board"
Error 27 occurs when rental vehicles are not properly STLinked or an incomplete firmware dump is used.
It can also be caused by using an old serial change method.
To temporarily fix, hold down the brake and throttle on boot up and release once it beeps.
Changing the serial number twice using a newer dAuth supported serial change method.
If that doesn't, flashing a CFW using cfw.max.sh with error suppression enabled will also solve the problem.