If your dashboard is Co-Term you would continue ordering LIC-ENT-XYR parts as necessary. If you are swapping APs you can reuse the old licenses.
If you have Subscription or EA, you need to provision the new Unified Licensing. For Subscription you need to add (or value shift) the qty necessary. If you have an EA and are midterm you just need to have a single license provisioned to activate the suite and then your next true-up will capture the net changes.
If you are brand new to Meraki, I would go with the subscription as that is the recommended path forward.
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