I had the same situation when I tried to bid on an upgrade last night. Used correct booking number.
Message said I wasn't eligible to bid for an upgrade and to try again. Cruise is paid in full, sailing Dec. 21, 2022, 7 night. When I called last week to purchase an upgrade, princess rep told me there were lots of cabins. So I got on princess chat and they said because I have already paid in full, not eligible. Doesn't make sense, that is not what is posted by princess on rules to be eligible
May be a glitch in system?