Melodyne with Audacity ALMOST works.

Melodyne Essential 5 ( I bought it for $50)appeared as plug in Audacity automatically, window opens, but file doesn’t go in Melodyne window.
I would pay for Audacity version, which can accept Melodyne!!!
I am going to make a video on youtube, same screen name there.

Technically, it’s up to the plug-in developer to make it compatible with various hosts.

The Celemony website says:

Which DAWs are compatible to Melodyne version 5?
We test Melodyne regularly with the following DAWs. Please note also the tips and advice regarding the DAWs in the online user manual.
• DAW System:
◦ Reaper
◦ Logic Pro
◦ Pro Tools
◦ Cakewalk by Bandlab
◦ Live
◦ Cubase
◦ Nuendo
◦ Digital Performer
◦ Samplitude
◦ Mixcraft
◦ Studio One

Very few commercial plug-ins are officially compatible with Audacity (but sometimes they work). I always assume that’s because most Audacity users don’t want to pay for anything. But maybe there are other things about Audacity that make it “hard”. There may also be issues combining iLok (or other anti-piracy) with open-source applications, but that’s also just a guess.

With free plug-ins it’s usually hit-or-miss, and obviously the developers don’t have the budget to test & debug with every audio editor and DAW.