I know, but when I go to manage booking on the SQ app/website I get this:

So I am hoping, that even though I can’t select a seat on SQ’s app as it’s an NZ codeshare flight number, that I’ll still be able to book the cook in the app closer to the time of departure.

As I mentioned earlier the seat selection was fine on SQ’s app for my other SQ flights though, and for this particular flight I selected a seat on the NZ app with no issue.