When I am trying to plot a single layer, using the exact same line of code as provided by the author, it is somehow showing only a red picture. I typed the coding in Visual Studio Code as below:

import os
os.system('py gcode_reader.py -t 1 octo.gcode -l 1')

However, the output is as below:

It is the same no matter which layer I specified. The output is the same as above even if I changed to the 40th layer.

What may be wrong? I would appreciate any help.