Originally Posted by
ESpen36
Now, if your upgrade clears and then you try to check in (via OLCI, kiosk, TA, GA, AAngel, etc.) and you do not have enough upgrade credits and are sub-EXP, then the system will stop you and force you to buy upgrades or give up the upgrade. But until the moment of check in, the system doesn't care whether you have enough upgrades or not.
Or, the system will stop you and force you to buy upgrades, period. Giving up the upgrade may not be an option; I learned this the hard way when I had an upgrade clear which I had requested weeks before, and in the meantime had run out of stickers. I had to buy stickers before being allowed to check in. Not ideal, but I considered it a valuable lesson learned for $60 and then sat back and enjoyed my wine.