I have a MAC version 10.13.6. , Audacity version 2.3.1.
Every time I attempt to download a plug in, it downloads to my download folder. Then, when I click it, it immediately tries to open in audacity and I get the message attached here.
It doesn’t matter the plug in, I always get this message.
Am I dong something wrong? Any help would be great. Thanks so much!
-Shelley

First, download Audacity 2.3.2. It will help you install nyquist plug-ins (such as ‘compress.ny’). See this page in the manual for help installing nyquist plug-ins.
Other types of plug-ins (VST, LV2, LADSPA) must be manually copied to Audacity’s Plug-Ins folder.
Copy the following line of text:
~/Library/Application Support/audacity
In the Finder, click on the Go menu and choose Go to Folder.
Paste the text into the dialog and click Go. You should see a “Plug-Ins” folder inside the “audacity” folder. Drag and drop the plug-in from your Downloads folder into the Plug-Ins folder.
Once you’ve got the plug-ins in the right place, you need to enable them in Audacity.
– Bill