They want you to buy it if you are using it in a SD-Access network however at the moment DNAC has no ability to assign the license. It was explained to me that, at least at the moment, the license is validated by the honor system. We have a license for our IoT device and DNAC Licensing still shows the device as "Unknown". The bottom line is yes you need to buy one to be compliant but there is no way to validate.
HTH,
Chuck McFadden
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