Unfortunately, my plugin didn't log any message here (that could be good or bad, just trying to trace here).
Please check the following:
My plugin is enabled in the plugin manager
You are in the game's main menu (where you can select Items, Skills, Equip, etc.) when pressing F9
In your game project's directory (where you can see data, img, audio, etc.), there's a new folder called "uicustom" which was auto-generated by my plugin
If that still does not work, try my plugin in a fresh new game project.