Found the solution, in the worst possible way.
From what we can see, you have to put the referral serial code in on the City of Heroes website, then sign into the game, and pay for the month of VIP.
According to my friend, the store implied (to them) that they should activate VIP first, then enter their code.
So, others referring, be warned: This bit of arcana is best clarified before your friend rushes to buy themselves a month of playtime.
Tell him to try contacting support - they may be able to help apply it despite the mixup.
Orc&Pie No.53230 There is an orc, and somehow, he got a pie. And you are hungry.
www.repeat-offenders.net
Negaduck: I see you found the crumb. I knew you'd never notice the huge flag.
I handle my susbscription through Account Management on the ncsoft.com website, not in-game. When doing it that way, on the page where you enter your billing info, the last item is a box for the referral code.
Your billing info and referral code are entered at the same time, not one before the other - in the case of the website, at least.
@Roderick
I've convinced a friend to sign up for a month of VIP! Hooray!
I've sent them the referral code for my free month! Hooray!
They put it in the store, and were told "Invalid code"! Boo!
...where are they supposed to put the referral code to get their bonus points (and not coincidentally, my free month...!)?
Thanks in advance!