I was moving devices from a c8 hub to a c8pro. When I tried adding my matter devices, I got this error, Pairing failed @ SendNOC with code 126 (Trying to add a NOC for a fabric that already exists). What I read was that the hub had the same fabric id as the old hub so I did a matter reset. I then started getting pairing failed @ findoperationalforstayactive with code 201 (no shared trusted root). I have tried resetting matter devices, Rebooting hub. Devices will then add back to Samsung smartthings, but keep getting this error when trying to share back to hubitat.
was really hoping someone would have seen this before… I can’t seem to pair it with hubitat at all. I’ve tried to pair it through smart things and directly through the hubitat app, but get the same error every time. I’ve reset the hub, reset the smartthings hub, factory reset the fan, rebooted hubitat, can’t seem to figure this one out.
I’m currently working with Hubitat staff on what might be the same problem. What Matter devices are you trying to pair?
these are Altitude brand ceiling fans
@gopher.ny and @bcopeland 
As a workaround, please download firmware 2.4.3 using this endpoint:
http://hubs.ip.address.here/hub/advanced/downloadPlatform/243
Then use Hubitat Diagnostic Tool | Hubitat Documentation to switch over the that version. Pair device using 2.4.3, and then switch back to the 2.5.0.
The “Trying to add a NOC for a fabric that already exists” message may provide a clue for us, I don’t recall seeing it before.
Unfortunately, this did not solve my issue. However, the error code has changed with the switch. I am now getting stuck at sendNOC. Pairing failed @FindOperational with code 50 (Timeout)
Just as information. I wanted to see where my issue was, so I also shared the device from smartthings to an instance of home assistant that I have. It did add to home assistant. I then tried to share from home assistant to hubitat to see if that would make a difference, but got the same message.
Thought I had figured something out. I was able to add the device. After added, changed to the appropriate driver and had everything working. A little while later, couldn’t get them to work with hubitat. Removed them and back to the timeout error
I have three of these fans. the frustrating part is that all three have been working mostly flawlessly for months. never had this much issue adding them in the past. we moved last year and I brought my c8pro from the old house. I was just trying to update the system here with the c8pro.
Just wanted to give a quick update for anyone following. It seems like I can get the fans to join hubitat through matter one at a time. I’m having to shut down the hub and unplug it and then it gets past the SendNOC. However, either the next time the hub is rebooted or potentially just over time, it loses connection to the device. It doesn’t seem to lose connection to other services, but hubitat is the one I need/want.
any other suggestions? I’ve tried going back, but still having issues with Matter. I haven’t switched back to 2.5.0 yet
Well, It seems if I want to leave my hub connected via wifi only, I can get matter to work. I’m not sure what the difference is, but that seems to be the case.
Well, not sure that anyone is reading this, but for anybody interested or those in the future, my problem seems to have been caused by my router. I am using a Linksys - Atlas Max AXE8400 Tri-Band Mesh Wi-Fi 6E setup. For some reason the default IPv6 firewall was blocking internal matter communication on ethernet. My understanding is that it is only supposed to be a firewall against external threats. I turned off this firewall temporarily and left the IPv4 firewall up and was able to pair my matter devices with hubitat. My other hubs all have a wifi connection so I assume that’s why they were able to communicate still. After connecting the devices with hubitat, I turned the firewall back on and the devices would not work again. Turn it off and they work again without having to reconnect them. I may be looking to upgrade routers soon. These are going on 4 years now. @gopher.ny @neonturbo @Ken_Fraleigh thank you for your help through this. I was on the verge of giving up.
I’m glad that you posted this. I was finally able to get my Tapo plugs to pair with HE by turning off IPV6 and the IPV6 spi firewall on my Linksys mx5600 routers. I don’t know why it didn’t affect my Hue Bridge Pro (ethernet), or Aqara hub pairing (or Tapo pairing with Apple Home), but I’m hoping that there isn’t a real need for the IPV6 firewall if IPV6 is disabled.