Having trouble pairing your Matter/Thread devices? Make sure you have IPv6 enabled. I had it off because my ISP doesn't do native IPv6, so I locked it down.
That was the primary source is my Matter grief.
Once I enabled IPv6 on my Home Assistant controller (set to "automatic") things went a lot more smoothly. Don't need any infra changed, didn't need to touch the router. Easy peasy: Just make sure it's on at the HA controller.