I think I know what the OP was trying to do.
Use Cura to directly print to printer, via Astrobox standing in place for Octoprint.
There exists a Cura plugin (note, a cura add-on, not a octoprint plugin) which allows one to click print in Cura Desktop and automajically connect to octoprint and get it printed and monitored. Basically the same thing as Astroprint Desktop -> Astrobox -> Printer, but instead Cura Desktop -> Astrobox -> Printer.
What OP was describing was the config window where one puts in some config to configure the “Connect to Octoprint” Plugin inside cura.
I actually found this thread when trying something similar - the thought process was - oh, if Astrobox was forked from Octoprint a while ago, maybe the Octoprint plugin may work with Astrobox!
BTW, I’m not able to connect and have been unsuccessful so far (I don’t even get as far as API key entry) so suspect poster may have done more to AstroPrint beyond a stock install (ie, turning on Octoprint-based discovery)