Hi Noa Dor,
Your product key to unlock the full sim should be in your original purchase confirmation email. It is a 24 digit code that is a combo of letters and numbers. If you cannot find that email, please email firstname.lastname@example.org.
Just a side note, when you do find your product code, X-Plane support will never need the entire number, so please keep it secure & secret like you would a credit card number. Support would only need the last 8 digits of it to help with any problems.