Ilok License Manger (updated) > Licenses menu > Redeem Activation Code > [BOX] [BOX] [Box] [box] [box]
All looks good to me to this point but can put only numbers in. I did some Googling but what I found wasn’t helpful and thought quickest/easiest would be here.
Copy/paste yields similar result in that only the numbers get entered (in sequence as if the letters don’t exist)
Code is for Cubase 10 Pro.
edited to include copy/paste results