Auto upgrade with not enough miles balance
 

Does anyone have experience on what happens if you auto upgrade with not enough miles in your balance and a seat in the higher class becomes available? do they cancel the upgrade or give you the chance to buy the miles difference? To be honest, I am not going to buy miles in advance if in the end I do not get the upgrade...
Thanks for your feedback
Docsxx

I actually just signed up to try and see what happens because I've received 3 alerts of availability only to login and see none. Not sure what happens but nothing to lose at this point

You can still register for the auto upgrade. When an upgrade seat becomes available you will receive the email but it will not allow you to execute the upgrade until you increase your balance. Recently I had the same situation where I was 1000 points short. I quickly bought the points and then executed the auto upgrade offer.