The wheels keep spinning every couple second after the machine powers on, and indicates an error, how to fix it?

If the wheels in the hopper are consistently spinning after the machine powers on, and then stop with the “hopper sensor error” or “main motor error”, the hopper sensor is too sensitive. 

Please use a dust-free cloth to clean the Hopper Sensor shown in the picture. If the problem persists, please contact us using the contact information below.
Email: support@munbyn.com
Phone: +1 650 206 2250