These add-on's are only for use with Studio One or as VST3/AU/AAX, these do not work with the 1818VSL Control Panel Software (now discontinued).
INSTALL IN STUDIO ONE
Download the Add-on installer if you want to user the Add-on with Studio One. Once the download has completed, launch Studio One, then drag & drop the file into the Studio One application window and follow the onscreen instructions.
INSTALL IN PRESONUS HUB
Download the PreSonus Hub installer if you want to use the VST3/AU/AAX versions of this plug-in. Once the download has completed, locate and double click the installer file to start installation, and follow the onscreen instructions.
If you need further assistance contact support at https://support.presonus.com