Have you looked in Help > About Installed Plugins, that will tell you what the status of the plugin is. Also, the last two digits of the plugin version number should match the last two digits of the DAZ Studio version you are using. For example, my GoZ plugin is DS4_GoZ_1.2.0.90_Win64.exe, and it is for DS4 version 4.5.0.90, other versions of the plugin wont work.
You should probably re-download the the latest ZIP file for DS4 from the site here by resetting your download from your order history page.