Procedure for invalid keys received?

post in the giveaway your key doesn't work, wait till the ga creator sorts it out.
if not, mark as not received and move on.

Happened to me twice from the same humble bundle that my gift links had been activated. Winners contacted me, I contacted humble bundle. Humble gave me new links that I gave the winners.

It took a little longer and a little more aggravation than we'd all expect, but it was resolved quickly and amicably