north stratus
Recently I tried to add a new Matter over Thread device, but unfortunately it failed with the following error (see screenshot).
I had already a border router (open thread border router) configured and other devices connected to it.
How can I debug the issue, and what steps could I go to add the device to my network?
hybrid cliff
The most common reason for this error is that you missed step 3 of https://www.home-assistant.io/integrations/thread#case-1-making-home-assistant-your-first-thread-network (didn't load thread border router credentials onto your phone)
It's also possible there's an mDNS problem. You could try enabling the "Beta" option in the OTBR app - that uses a different mDNS implementation with better compatibility.
north stratus
Thank you @hybrid cliff syncing the tread credentials does the trick. No idea, why this was necessary again, as I had added two other Matter devices with the same phone before.