Hello! I was able to test this and it is working as expected on Ren'Py 8.5.3, the latest release - I suggest updating if that's possible. I also didn't have any problems running it on 8.3.7. If you're still having trouble on either of these versions, make sure you can run the example code in a blank project. The problem may be with where or how you're trying to use it if it's still not working. I hope that helps!