Which version do you have, 7.70 or 7.73?

Normally, you need only assign the material and set the 4 skills that the material needs, this is the example in the manual:

#include <mtlFX.c>
...
action toon_warrior()
{
my.skill41 = floatv(50); // Shadow
my.skill42 = floatv(50); // Edgewidth
my.skill43 = floatv(50); // Threshold
my.skill44 = floatv(50); // Smooth
my.material = mtl_toon;
...
}