Hi Capitano
I'm not with Laminar Research, just a fellow simmer in the UK, but when you say that you 'bought the box' presumably you mean the X-Plane 11 DVD set, having already tried the digital demo download?
If this is the case and you are trying to use the X-Plane 11 DVD set, then no Product Key is necessary, you just need to keep Disc No 1 in the DVD ROM tray, all the time you are using the simulator.
I hope that I have understood your query correctly, but should you have any further questions, please advise?
Regards