I have the following line
Dear Iman,
Indeed, you are close, but missing one parameter that is computed based on the width, which is the area.
When using Python scripting, we need to define all linked parameters so if you add ("A", deadman_area) the command should be successful.
The moment you open the GUI (graphic user interface) the command is fully executed which then correctly computes the area in the background, leading to a valid material.