[ubuntu] No bootable device - While installing Ubuntu from USB stick on Mac

I want to dual boot linux and osx on my mac.

I followed this thread to create a bootable USB stick with Ubuntu on it. I've followed the exact instructions and everything worked fine but when I try to select my USB stick to run in rEFind I get this error

I've done this a bunch of times and I'm at a loss on what to try next. Any help is really appreciated.