I just posted this is another thread:

Be aware they don't all work as OTG devices. I have a Seek thermal camera that wouldn't work on my 5X with 3 different brands of C-to-micro adapter, but then this one finally worked

The one /u/ddp337 linked to says right in the specs that it doesn't do OTG. Nice that they put that in there, I didn't even know to look for that until a few days ago.