As mentioned above - you have to claim the device in the Dashboard:
https://documentation.meraki.com/General_Administration/Inventory_and_Devices/Using_the_Organization...
You can do this using the serial number(s), but it's generally better to claim using an order number, if you can, as this claims both the devices (all the serial numbers) and any license key ordered concurrently, in one go.
You may find, if you've claimed an individual serial number separately, you're unable to claim the order number later, so I'd get in the habit of claiming by order number, as soon as you know it. Serial numbers (and license keys) are always of the format xxxx-xxxx-xxxx, where the xs are alphanumerics. Order numbers are shorter and contain no hyphens.