Got this info from chat, told to phone up to resolve it:

“Upon checking, the reason why you're getting the error 913 is that your device does not support or is not configured to use SMBv2 or SMBv3. SMBv2 or SMBv3 is now required, as we no longer support SMBv1 and HTTP for music library shares.

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• Rest assured, we do have a workaround for this."

Rang up bang on 8am, wait time 5 mins, waited 40mins, got through to a Sonos tech help guy, set up a remote access session and it ended the after 2 mins “due to connection issues”; my phone had full signal and I have a solid wifi connection. Phone wait now 45mins.

Incremental progress but no solution. Infuriating. And no media coverage?!