URL mapping to internal page question

I am trying to connect an internal page of my site to its own unique URL. For example: I want specialsite.com/kittens to redirect to just kittens.com.

I followed the instructions in URL mappings so the slug of the disabled internal page has a 301 redirect to the unique URL. But when I enter that URL into my browser, I am still sent to the homepage of the main site.

Both URLs were purchased third-party and are connected in my domain settings. Should I have both domains connected? Or should I just connect the main domain and leave the internal redirected one out? Or could it be a different issue altogether?