Booked for 3 passengers and one of us can no longer join in our flight since his passport renewal was delayed. The site wouldn't allow us to go to the next page as we had to input ALL passport details but we simply couldnt as we dont have the passport yet. They cant cancel him and insisted we should still check him in with a DUMMY details and just mark him as no show. I checked on the airlines guidance and its clearly indicated not to check in any passenger who isn't flying. I told them its not best practice and that I checked-in the airline directly and they said they wouldnt help us in case something happens since we booked it directly with the airline.