My bike is Ancheer. The cable that connects the controller and the electric motor came off as soon as it started. But if I keep the rear wheel in the air, the cable does not disconnect. The wheel spins. What is broken? How to fix it?
It sounds like your rear axle bolts are loose and need tightening.
When the wheel is on the ground the bolts are not tight enough, so the motor spins the axle and disconnects the cable. When the wheel is off the ground, the loose axle bolts have just enough grip to spin the wheel instead of the axle.