It was simply a matter of setting the port correctly, making sure I had a user and folder on the NAS server that I could store the data in and then starting the sync. If I recall correctly the initial sync took a LONG time to run and everything had to be stable (no using the mobile devices, not working in OF at the time to add or modify stuff etc.)
On the onmifocus side I use this as the sync location
Oogie is the name of my partition on the server. The final / was critical as I recall. It’s not supposed to be needed according to the documentation.
The file there is called OmniFocus.ofocus
My Devonthink Database sync is called asgard_sync.dtCloud and it’s at the same location https://asgard.local:5006/Oogie/
Make sure both the NAS and the machine you are starting from (In my case my iMac) ar eon the same wifi network and to get it running open up a finder window with the partition on the server in it by selecting locations and then logging in to the server.
As I said I set it up so long ago and it just owrks that if there was nayting else that I had to do I don’t remember.