[GRASS-user] v.extrude not changing anything

I have a 2D vector map which is actually a single line (it shows a coastline). I try to give to this fixed height and make it a 3D map (the line to become a wall).

I try v.extrude --overwrite input=COASTLINE@final output=coast_3d@final height=10 type=line but nothing changing at all (then I export this in .vtk and i check it out in 3D software).

Is it something I am doing wrong? I do what the manual says! Is there another way to do the same thing?

Thank you for any tips.