In the render tree you will see a "Toon Paint and Host" node. Even if your spotlight has "shadows" enabled you will still see no shadow that the objects cast onto the ground. Do a test render to see that.
Now add a "mix_2_colors" node as well as shadow node (nodes > illumination > shadow) and a constant node. Then connect the constant into the RGB of the shadow node. Make sure that you set the constant color to a dark color. The rest simply connects as shown in the image below: