Problem with PMW3901

If i run the motion.py example, i got the following error:

Traceback (most recent call last):
File “/home/pi/breakout-garden-master/pmw3901/examples/motion.py”, line 21, in
flo = PMW3901(spi_port=0, spi_cs=1, spi_cs_gpio=BG_CS_FRONT_BCM if args.spi_slot == ‘front’ else BG_CS_BACK_BCM)
File “/usr/local/lib/python3.7/dist-packages/pmw3901-0.0.1-py3.7.egg/pmw3901/init.py”, line 45, in init
raise RuntimeError(“Invalid Product ID or Revision for PMW3901: 0x{:02x}/0x{:02x}”.format(product_id, revision))
RuntimeError: Invalid Product ID or Revision for PMW3901: 0x00/0x00