godaddy URL shortener - Where to forward (sub)domain to work with the shortener

I'm trying to use the URL shortener (https://shortener.godaddy.com).   

 

It now requires custom domain or sub-domain (rather than x.co, etc) - and to get that to work it says that you need to forward the domain / subdomain.   However it doesn't say where you are supposed to forward the custom domain subdomain to.  

 

So, where should I forward my domain / subdomain to in order to get it to work with the shortener

 

I was on the phone with support for awhile and interestingly they logged in he still had the old option to use shared domains (x.com).