Strange one, just booted up a new C4 hub, it's taken an IP address but it gives a "ERR_CONNECTION_REFUSED" and the Hubitat portal can't find it.
Port 8081 only shows "Hubitat Elevation Update Tool" and nothing else (i.e. not the usual diagnostic menu).
Tried various browsers and different PCs etc.
Any thoughts?
Also tagging @bobbyD but no rush as I'm out for the rest of the day now:-)
I'd guess it's the vintage of platform OS that is on those older C-4.
I just got a c-5 and it came with v2.1.5, so not terribly old, but I bet the c-4's have been sitting on the shelf quite a while now. 
Also, they come with only the one platform OS, so there's nothing else to switch to... (I'm going from memory.. my memory of that menu with just the one function.)
Yeah was kinda thinking the same .... hoping support have some ideas to resurrect it!
As stated above, I suspect that you may be experiencing the cloud-connectivity issues (this would include the ability to download new firmware) that you'll see if using a firmware before 2.1.4.130 after October 1, 2019 on a C-3 or C-4 model hub. I'm pretty sure new C-4s are basically special-order-only at this point and I'm not sure what firmware they would have. If yours has been sitting at home on a shelf for a while (before August or so, I think), though, it's likely it's older. 
The fix is documented here:
However, the Portal should still be able to find your hub--and is a necessary step to get the firmware up-to-date so the regular process works again. I'd give that page a read just in case there's anything you might be missing. Otherwise, I see you've tagged Support, so hopefully you'll find a fix soon!
@bertabcd1234 ah yes, I recall that post now ..... but unfortunately this is a new C4 that I only ordered last week, I wanted a couple of C4 as cold spares for my existing C4.
It's been so long since I set my first C4 up that I can't recall what the out-of-the-box behaviour is.
Should a "new" hub (irrespective of version) be accessible via IP straightaway? OR do they ship with a base firmware just to boot and register to the Cloud and be updated and thus won't respond at all?
If so then It sounds like these might be in no-mans-land .... they can't be registered because they're not up to date, they can't be updated because they're not registered?
I have a new C4 that I hadn't even opened the shipping box yet. So I set it up and have the same issue. Following the instructions from Cloud Connection Unavailable After October 1, 2019 [SOLUTION], I login and go to 'My hubs' and the new hub isn't listed. Under 'Find hubs' I use the Advanced button, put in the new hubs mac address which locates the hub, but it can't be added to 'My hubs' since you can't open the local interface.
Suggestions?
Wait for support by the sounds of it, maybe they can manually register them on their side and then they can be updated following those other instructions.
Hi there. Sorry for the troubles. If you didn't do so already, please send us an email to support@hubitat.com. Also, in order to speed up the resolution time, please be sure to include the following details:
Also, please be sure to use a supported browser and operating system.
The new C4 hub is now up and running after emailing support and following the directions provided. I'm not sure if something was required on the back end for it to work, so I'll let @bobbyD post here if the instructions will work with having to contact support.
Both of my new C4's are up and running too after a prod in the right direction from Chuck @ HE.
Download the Hubitat app
