OK OK OK Ok Ok OK I think i have this error code (-6722) soughted.
This is what i found out.
Ensure keychain is on each device and make sure two factoring is set up on each device YOU OWN!
Check for any updates they should come up on all the devices that need updates relating to the 2 factor and address accordingly have another device close by to add verification codes....(disclaimer :this process will **** the kids off so have bribes ready!)
I had to dig out an old Ipad because the account check was going to that ipad....annoying but necessary.
Once you have every ipad, ipad pro, iphone, mini pad iphone X and MAC on the same settings all linked all running same IOS or the latests for that device there should be NO issue connecting the device.(well error code (-6722))
After making sure I'd ticked all the boxes above I walked up to HOME POD and the setup window came up (press setup) and next thing i know its asking for its location eg Living Room.
If you get this far look for the app that looks like a HOUSE (home app) and away you go with further setup.
THIS HAS TO BE IT!...
Well it worked for me and yes grrrr....6 hours of my life i won't get back.
Apple expect a bill in the mail.