Hi evehal, thank you for the kind words!
I don’t believe this plugin plays nice with the engine’s plugins folder, you have to install it directly to your project’s plugins folder to guarantee compatibility. First make sure you have the right version for your engine version (I just uploaded the build for 4.15, so that may solve your problem!) then make a folder called “Plugins” in your project’s root folder if you have not already. Then copy the “iTween” folder inside the archive and paste it into the Plugins folder you created. If you’re on Windows, you can use the included iTween for UE4 installer and simply choose your project folder - the installer will handle the rest.