Setting Up WHMCS with Subdomains

Hi guys, I appear to be missing something while trying to setup WHMCS 5.1.2 to use subdomains. Let me run down what I have already done and provide you some screenshots. I had no issues setting up servers under WHMCS, most of my questions are setting up the products.

Starting on the Details page:
In order for someone to have the option to register a domain or use a subdomain I must check Show Domain Registration Option. If not, once they click order they jump directly to review/checkout and they are never given the option for Site title or the ability to pick their subdomain name. But when that domain registration option is selected the subdomain is not shown, it treats it like a top level domain registration even when subdomain is selected. It does not allow me to progress past this page.

My module settings include the subdomain and I have left unchecked Use Domain Field because I would like to use the domain mapping plugin per the install instructions.

The Default Blog Domain setting confused me a little, the first time I started with a and that didn't help. Neither did removing the period. And under Other settings I added the subdomain with no luck.

Am I missing something? I would like to keep all my hosting info and support in my main WHMCS install if possible but perhaps I need two installs, or just use ProSites. Thanks for your assistance.