Upon creating your very first Confluence space on the free plan the wizard will guide you through the setup with an example space which you can name and set the Key for.
However, this space is setup without admin groups that you are part of or have access to, namely: Confluence Analytics (System), Former user, Chat Notifications
So even though I'm site admin and can add myself to preset groups like site-admin & administrators, I cannot add any users or groups to this space nor even see the manage permissions button, even though I supposedly am listed as its creator. So I'm now stuck with this space that I cannot manage and that has burned the project name & key which I need.
Note that when creating new blank spaces everything is setup fine and dandy and I can access and manage everything just fine. (as far as the free tier allows)