i'm having a problem with the particle_type variable

could possibly be that 0.0 is not a valid number. If that's the case it needs fixing.

did you change that yourself? What version are you running. Cannot replicate this issue even when manually changing the particle to the values you have.

I'm having the same issue but with different values.
My values are:
dust 0,7 0,2 0,3 1

My versions:

• Minecraft 1.15.2
• carpet mod v1.3.9

Edit:
after executing
/script in camera run global_color_a = str('dust 0.5 0.5 0.5 1')
/script in camera run global_color_b = str('dust 0.5 0.5 0.5 1')
the particles are shown.

The error does not exist in version 1.3.16

yes, because it was fixed. Please use the updated version