What exactly makes a referral ineligible?

Hello, I recently invited a friend and a family member to join dropbox and both of them appeared as ineligible for the referral program after installing the desktop app.

I read other threads on the same topic and I can already state that, according to both of them, their e-mail address was never used for a dropbox account and their respective pc never had a dropbox installation previously (but I cannot verify this myself).

I have never shared an ip address with the friend invitee but I may have occasionally used the internet connection of my family member. Nevertheless, I don't think I should be tagged with this ip address in dropbox database. Since the problem occurred with both invitations, I presume it's not linked to the ip address.

Would it be possible to have more details on the reason for ineligibility on the referral page and, ideally, a button to appeal directly there? That would prevent so many users from posting threads here for the same question/problem.