Usually you get a message that the device is already added to another organization, which doesn't seem to be the case for you.
But if that's the case, there's nothing Meraki support can do.
Did you buy it second-hand? If so, you need to contact the person who sold it to you to remove it from your current organization.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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