I don't use FreeNAS (FreeBSD?), but did you install the plugin from here?
https://community.getchannels.com/dvr#install-freenas
If that doesn't help, I'm sure a FreeNAS user or one of the developers will reply.
DVR Requirements https://getchannels.com/dvr/requirements/
If someone gave me an ELI5 explanation on how to get started, I probably wouldn't have learned as much as I have, but it would have been quicker to get up and running. I agree a WiKi or the like would help new users and ease the support burden for FAQ's.