28.01.2018 23:10
Usually, a serial number can be found in your email box. If you accidentally deleted an important message, you can sign in your Unity account.
Now you have to assign your seat by clicking on Organizations → Manage/View → Seats & Services → Manage Seats → click on your name → Assign 1 Seat(s).
Accept your seat assignment and check your email. There will be your serial number.