We host on premise and expose our website for events and such.  I was finishing up the email marketing part and we ran into this error when accessing externally:

ValueError: Setting 'domain' for a cookie on a server running locally (ex: localhost) is not supported by complying browsers. You should have something like: '127.0.0.1 localhost dev.localhost' on your hosts file and then point your server to run on 'dev.localhost' and also set 'domain' for 'dev.localhost'

This occured when the UTM parameters were added to a link.  The resolution despite the message was to set the upstream host in NGINX to the full domain name.  As in:

	upstream mydomain.com {server localhost:8069;}

Debugging into http where the cookie is set was the most useful part that got me to my answer.

Hopefully this will help someone else.