This will not work, the endpoint is for Meraki devices, not arbitrary client devices such as PCs etc. URL: https://api.meraki.com/api/v1/devices/MZ00AVWF There is no Meraki device with that serial number, so you get a 404 response. If the PC/whatever is managed by System Manager, there're a bunch of endpoints to get/set various info, for instance https://developer.cisco.com/meraki/api-v1/modify-network-sm-devices-tags/ I don't recall seeing an endpoint that updates notes/tags info for non-managed clients, if there were one I'd expect it to be based on the Dashboard generated client ID or client MAC, not the client's native serial number.
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