Crystalsky is not the same as a
Smart Controller, however my experience might give you a clue as to where you might need to look for a serial number. When I entered what I thought was a SN taken from the label on the back of the device, this was rejected as invalid. Eventually found it in the
Crystalsky's 'Settings'. Maybe completely different for you, but a little lateral thinking may help you find what you need.
While I am still experiencing issues with user authentication failure when trying to validate the unlocking license, I have to say DJI were very quick - within about half an hour - returning an 'unlocking license' after I had submitted my request.
Teething problems with DJI's Fly Safe? Maybe. At the moment the process seems to be an exercise in absolute frustration, in part because I feel DJI have gone at implementing the Fly Safe model too hard too fast. I suspect some of this may be attributable to some well publicised events, along with too many less publicised instances of UAV's not been flown responsibly. If there is pressure coming on DJI to implement a global NFZ with a system of individual licenses being granted on an application basis only, I suspect the AIOC may be the body with sufficient international clout to get such a system across all geopolitical boundaries.
Don't like it much myself at present, but it is what it is - and probably will be the only way any of the UAV community will be able to fly in the very near future. "Cowboys" and impromptu misusers will simply not be able to get their bird off the ground. Remember, pretty much all the technology that has given our UAV's the ability to fly, is also very much the same technology that can be used to prevent those same UAV's from flying.