Problem using VMTK

Operating system: Windows 10
Slicer version: 4.9.0
Expected behavior:
Actual behavior:

Hello everyone,
I’m trying to use VMTK to create a model of some blood vessel from an MRI study but even though I’ve seen and tested with all the tutorials that I found I still do not get anything.
Does anyone know what I’m doing wrong? I leave you a capture.
Thank you very much!

What do you do exactly? What do you expect to happen? What happens instead?