If a Meraki device is already claimed in another user's network, it will not be claimable in another organization. If you attempt to claim a device that is already in a network, you will receive an error message reading "Some of the devices you tried claiming are in use"
Due to privacy and security concerns, Cisco Meraki support cannot assist in moving devices that have already been claimed. In order to add the device to your network, you will need to contact the original owner of the device, and have them follow the instructions in our documentation to remove the device from their network. Once that has been done, after a brief wait (around 15 minutes), the device should be claimable again.