My interaction key wasn't working, and I obviously couldn't rebind it because I had nothing with which to select the option.
I deleted the config file and started over again. I realized afterward that I'd plugged in a new peripheral, and that perhaps it had been interfering.
But whatever caused it, once FlyInside loses the interaction button, there's no getting it back. I think it would be a helpful feature to have a failsafe reset method for the interaction key.
Product is working fine on my Vive; very glad to be in the air again.