Originally Posted by
sea_flyer_17
A family member asked and I wasn’t sure- they have about $60 in credits expiring. Can they use them to pay for Comfort+?
Not possible for online seat upgrade FCM offers. Only possible when doing an upfare for itin to C+ by going through Change Flights option and paying the fare difference from coach to C+. You can upfare each one-way direction independently on a roundtrip booking, but generally not invidual flight segments like FCM offers (since all flights in each one-way direction are generally booked on a single fare component).