I remember when i was in LAX last december i have an I class fare LAX-MNL , I was able to pay 1 segment ( LAX-HKG ) upgrade Business to First upgrade for $ 1,510.00, HKG-MNL in Business.
Then, this year January when I came back I took MNL- HKG in business class and while I was the lounge, I asked the agent if I can pay the upgrade difference from Business to First she said " NO" coz my ticket is I class. I forgot to ask her how come when i was in LAX I was able to pay the upgrade? Do you know guys why? Thanks