Originally Posted by
higham44
I have entered that too and get a similar response from the website. Strangely, I have a flight from PVG to HND on JAL and have managed to book seats using the alpha-numeric code.
I think the transition is still a bit in chaos. But if your number is still QR813 on the HND DOH route, then more changes are still to come as the codeshare flight number on JAL is different from that. If it is an avios booking, you will probably be moved to the NRT DOH flight instead.
But until the booking gets the proper flight number you probably can't do anything for seat selection, or until you are moved to the NRT DOH.