WHMCS Integration, Provisions and Domain Mapping

First off - WHMCS Integration: 401 - Unauthorized errors - how come?
Second - I'm a bit overwhelmed. I installed and configured a new WHMCS install. Am wanting to integrate it with my swartist.com site which needs to allow users to sign up for a monthly membership, capturing their email/name/etc and allowing them to ask for a new domain or a subdomain on my domain.
I've followed the install logs on wpmudev and whmcs and am just not sure how to make sure it's all working seamlessly.
Thanks