Mine works fine in the free SketchUp 2017 Make :)
I don't know for upper versions...


Curves must be "closed"

PS I have seen the link above works for 2021! :)
for convert a file to "rbz" just zip your folders/files say ferrari.zip and rename it ferrari.rbz
for more easy install!

So put the folder FerrariSketch and file Ferrari.rb inside a folder Ferrari
Zip it, rename it Ferrari.rbz