WINDOWS USERS ONLY
To add the Slate Digital default VST2 plugin path in Studio One 3, please go to the "Studio One" drop down menu and select "Options".
Select the "Locations" tab and select "VST Plugins". Click "Add" to navigate to the following plugin path(s)→
If you are running Studio One in 64bit: C:\Program Files\Vstplugins
If you are running Studio One in 32bit: C:\Program Files (x86)\Vstplugins
In some cases you will need to force Studio One to rescan all plugins at start-up. To do this you'll need to navigate to "C:\Users<username>\AppData\Roaming\PreSonus\<Studio One version>" and temporarily relocate the "x64" folder. This will clear your Studio One preferences and manually force Studio One to rescan all your VST Plugins.
MAC & WINDOWS
Go to the "Studio One" drop down menu and select "Options". Under the "Locations" tab click "Reset Blacklist".