Originally Posted by
navatwal
I believe you cant upgrade a reward seat with miles.
It has to be a cash purchase
Just for reference, it's the other way round, as Nick said -- you can upgrade a reward booking (or mileage upgrade) with miles (except for the Amex PE upgrade vouchers, as I think you discovered!). You cannot generally do it with cash, although sometimes it seems to be possible at the airport.
Well done on the upgrade. ^