There is Power CMS Builder which is the extension that the copy you reference comes from. prior to that being released, we offered Power CMS the Solution Pack
As a Solution Pack, the license offered was for 1 Domain. This was the version you purchased, and the license you agreed to at the time of purchase.
Power CMS Builder, the Extension, was not available at that time.
I see in your order history you have previously purchased Super Suite, this would mean you have an upgrade option to purchase Design Extender (Which includes Power CMS Builder with it's unlimited domain license) for $99.99