Symptoms

I do not seem to have the ability to Register my old dev site. It says it doesn't exist or something to that effect.
 

Diagnoses

The environment had recently been migrated from Development to Production perhaps some part of the registration wizard / app was targeting an old URL.
 

Resolution

Entering the Appit URL that the vanity URL points to (oKUID].appit.com can be found in the dropdown) allowed the registration wizard to continue successfully. Testing on another site did not require any changes for it to work.