Originally Posted by DMPHL

I've had the opposite experience. On an LAX-JFK red-eye, I was #1 on the upgrade list with Miles + Co-Pay. I'd previously asked the gate agent (as it looked like to chance of an upgrade) if she needed my credit card if it happened to clear, or if it was in the system. She said it was in the system and if there was a spot she'd clear me. Boarded and had settled into 11A, and the gate agent comes on right before departure, hands me my new boarding pass for 7D, and that was that. And the Miles were never actually deducted and the Co-Pay never charged.

So it seems the options, at the last minute when the flight is nearing departure, are skip over Miles + Co-Pay or just upgrade and don't worry about deducting.