Gold Cart doesn't show authorize.net payment gateway option

I paid $40 for the Gold Cart upgrade from WP e-Commerce from getshoppped so I could use my Authorize.net account for my online store, but when I go to the settings>store>payments page, authorize.net is not shown as a gateway option.

I am trying to wade through all the forums to figure out the issue, but I can’t untangle all of this. Does anyone have any tips for this?