Wish I had read the above advice earlier....
I booked award space on Iberia, connecting to Air Nostrum thru BA.
Went to Iberia site to enter API, which I thought I finally had entered correctly.
Went back today to change seat assignments, saw "More Info Needed" notations. Tried to enter more API info, no luck.
And now no seat assignments are showing??? Ugh!
Suggestions at this point??
Thanks!!