You can't upfare a single leg when segments are part of a single fare component (unless fare is broken). You need to be looking at married segment inventory availability, not individual flight segment inventory when on a single fare component and you want to upfare. The seat upgrade offers are not actually upfares (even though they change class on the segment that is upgrading) and are technically non-refundable and non-transferable. If you want to upgrade when there is no online seat upgrade offer, you need to upgrade (with an upfare) all flights on fare component (or break fare).
Last edited by xliioper; Sep 22, 2022 at 2:39 pm