Thanks for posting your solution! I'm happy that you worked it out :)
Author here. Could you try to run it from the console and paste the output here? I'm sorry, I don't own a Mac currently, so it's hard for me to prepare a working OS X build.
That's strange; there are still some Steam keys available on itch.io... Maybe that's a problem on their side.
Anyway, please follow me on Twitter (so I can DM you) or shoot me an email (my nickname here @thesecretpie.com) and I'll get you a key.
Please look for the "Request key" button on your purchase page.
