I had same problem.
I used to have Boot over a network.
This is optional:
Disconnect Mox from Omnia.
Maybe backup of tftp folder (not so necessary, because Mox tftp is in different folder).
Than revert changes from Boot over a network tutorial.
Reboot?
Than do a snapshot if you want (whatever seams reasonable to you).
Factory reset of Mox.
Try follow this guide:
Mox netboot requirements of DHCP (I think there should also be quotes at the end of the line „ssh-keygen…“).
That didn’t help me, because of a missing file.
So what I did next?
Disconnect Mox.
Revert to snapshot before netboot.
Factory reset of Mox.
Install Turris MOX network boot in Foris.
Create file C0A8018E.img CLI:
touch /srv/tftp/C0A8018E.img
Follow previous guide:
Mox netboot requirements of DHCP (remember quotes).
Reboot Omnia.
Wait…
If it still works you can delete file C0A8018E.img (if is still there).
And you can revert file permissions of /srv/tftp/pxelinux.cfg to previous state (just my guess no answer from turris team).