You scan the QR code, the app spins for a minute, and then: "Unable to connect." Or the device pairs and goes offline a day later. The good news is that Matter failures are rarely random - they almost always trace back to a small set of network settings. Here is the checklist that resolves most of them.

1. Enable IPv6 (the #1 culprit)

Matter relies on IPv6, and Thread-based devices use IPv6 exclusively. Many consumer routers - especially older ones - ship with IPv6 turned off. If it is disabled, Thread devices will fail to commission entirely, and even WiFi-based Matter devices can be flaky. Log into your router (see how to access router settings), find the IPv6 option (usually under WAN or Internet settings), and enable it.

2. Allow mDNS / multicast

Matter uses mDNS (multicast DNS, also called Bonjour) so your phone or hub can discover devices on the local network. If your router filters multicast traffic or blocks UDP port 5353, those discovery messages never arrive and pairing fails. Look for and disable any "multicast filtering" option, or enable "multicast-to-unicast conversion" if your router offers it. Make sure mDNS is not blocked by the firewall.

3. Turn off AP isolation

AP isolation (sometimes "client isolation" or "guest mode") stops devices on the same WiFi from talking to each other - which also stops your phone from reaching the device you are trying to set up. Disable it on the network your smart-home gear uses. For the same reason, do not commission Matter devices while your phone is on a guest network or a separate isolated SSID.

4. Watch the 2.4 GHz vs 5 GHz split

Most smart-home devices only join 2.4 GHz WiFi. During setup, your phone often needs to be reachable on the same network. If you have separate SSIDs per band, connect your phone to the 2.4 GHz network while pairing, or use a single combined SSID. See what is an SSID for background.

5. If you use an IoT VLAN, bridge mDNS

Putting smart-home devices on a separate VLAN is great for security (see IoT network segmentation), but it breaks discovery: your phone on the main LAN cannot see a device on the IoT VLAN unless mDNS is forwarded between them. Either configure mDNS reflection/repeating between the segments, or - if you do not strictly need separation - put Matter devices on your main WiFi to sidestep the problem.

6. Rule out a Thread border-router problem

If the device is Matter-over-Thread specifically, it needs a working Thread border router, and having several of them can fragment your mesh into islands that do not communicate. That is its own common failure - walk through how many Thread border routers should you have?

Quick recovery checklist

  1. Enable IPv6 on the router.
  2. Disable AP/client isolation and multicast filtering.
  3. Put your phone on the same (non-guest) network, 2.4 GHz if needed.
  4. Update the firmware on your router and your hub/border router.
  5. Remove the device from the app and re-pair.

For a one-stop reference on the exact router toggles involved, see router settings for a smart home.