When I squeeze the brake handle, a brake symbol with a exclamation shows up. Why ?

This is the brake sensor icon letting you know that it is stopping the motor from functioning while the brake is engaged. These bikes come standard with motor power cut inhibitors. There is a switch which cuts the power to the motor as soon as you engage the brake levers. When this happens you see a symbol on the LCD screen which indicates that this functionality is working properly.
Did you find what you were looking for?