it only asks for the last 4 of your social and they don't double check this..
you can make up the last 4 of the social it doesn't matter.
Just keep in mind you're limited. If you don't enter your social into the system, it'll limit you to make 15k. After 15k they shut down your shop and insist on getting it from you.
They won't report to your taxes until you hit the 20k mark though