Last update January 20, 2022
If plug-in you've just installed doesn't show up on plug-in list in Reaper first of all make sure all Software Requirements are met by your setup.
Try out the solution described in this entry at our FAQ. It's possible that some system runtime libraries required by plug-in are missing. This concerns especially relatively fresh Windows installations.
Still no success? Try doing full plug-in rescan in Reaper: