Apologies if this has been covered, as my search hasn't turned up anything.

Hoping to get clarification on an issue I'm running into trying to change a reward stay.

I have a five-night reward booking and, due to a change in travel plans, need to depart after three nights instead. Unable to make the change online, I started a live chat with a Bonvoy agent who informed me that, because my same room type is unavailable for the new dates (which all fall within the existing dates), I can't make this change.

I'm confused by this, as the room type is very much available *to me*, since I already have those nights booked! I just want to drop two nights off of my booking.

Is this actually Bonvoy policy? Is there anything I can do other than eat the cost of the nights I'm no longer using?

Thanks in advance.