Good morning! Sorry for the delay in responding, I'm currently on vacation.
I've tested the plugin and it's working correctly for me. Most likely, your plugin file is either corrupted or misconfigured in your project. I recommend doing a clean installation of it. You can even try it in a brand new clean project, make sure to configure everything properly.
I've attached on Itch.io a demo of the project I used for testing, and you’ll be able to see how the plugin works correctly with the plugin command.
I hope you manage to fix it soon ^^
Cheers!