So delete your account. I just got hired. Can confirm LinkedIn is irrelevant if you have a reference.
"Your LinkedIn profile URL (required):"
Just link to Reddit/r/LinkedinLunatics and lean back
HR is lazy.
Do you want to work in a company where HR is lazy to even work?
Don't have the luxury to pick.
Put in N/a
Put N/a -- see attached resume. If you have a reference, they will bother to review your Resume. You already have a high value endorsement from an individual on their team, plus internal hiring bonuses are good for team morale.