Website is already secured by Auth0, do we have to purchase the plugin?

The website we are attempting to set up in Median is already secured by Auth0.

I am having trouble signing, it's kind of working, but I am seeing some odd errors.

Do we have to purchase the Auth0 plugin if we have Auth0 set up on our site already?

If we do purchase the Auth0 plugin, how does that work seamlessly with the website to keep the website from forcing sign in? I'm confused how the plugin and the web will work smoothly together.