This error is driving me CRAZY. I booked a ticket for myself and now want to book my son a slightly different itinerary so I booked it separate with miles (FC). Except it won't let me. Different names, different FF accounts, different itinerary! But I keep getting the "duplicate" error and it won't let me book. 1.5 hour wait to talk to reservations (I'm Plat Pro if it matters). Total shitshow.