ShotGrid Toolkit: unable to download an attachment

Currently, I’m trying to create an application inside of ToonBoom Harmony that works with the SGTK API. When I am working with this, when I try to use self._sg.download_attachment, it seems to hang in the application and not know what to do with the “download_attachment” function. I’ve tried callbacks, log files, etc., and there are no errors returned that I can go off of. Is this function operational/compatible with ToonBoom Harmony to begin with?
I would like to download an attachment from a specified SG project to inject into ToonBoom, but by using SGTK, it doesn’t move past this function.
Any insight would help, thanks!