I tried on-line activation of a 64-bit plugin in Audcaity 3.0.4.
but get a message in the plugin GUI saying “CONNECTION FAILURE”.
[ Unfortunately this plugin does not have the option of off-line activation ].
Is this inability to connect, (safety precaution ?), inherent to Audacity ?, (or is it a Windows thing ?)
I don’t have any rules specific to Audacity in the firewall, and have tried turning my antivirus off when attempting to activate the plugin.
Trebor,
As a work-around, can you activate it in another DAW on your computer? I have done this before and once activated in one DAW, it is activated in all DAWs on my computer.
Mike
I gave that a go, even VST host, but no joy 
…
Try asking them on facebook, twitter or instagram (links at the bottom of their website).
I pressed the SUPPORT button on the GUI and sent them a message about it.
They emailed next day …
My guess is that not offering offline registration is an anti-piracy thing.
My guess is that your guess is correct 
Perhaps you could temporarily install Reaper and register it in that?
There’s a possibility that the plug-in may still require “phone home to verify” for it to run in Audacity, which would probably be impossible in Audacity.
I even tried disabling anti-virus & firewall 
This really is up to the plug-in developer. And for example, if you go to the WAVES, Anteres, or Celemony websites they have a list of officially supported hosts. Audacity is rarely officially supported… Sometimes they’ll work anyway but I assume most Audacity users don’t buy plug-ins so it’s probably not worth the trouble of testing and debugging or dealing with Audacity support issues. One of those (I think Anteres) specifically says that their plug-ins do NOT support Audacity.
With free plug-ins it’s usually just hit-or-miss because there is no budget for testing & debugging with multiple DAWs.