I have the LGT fare, I am sure of that mine booked into K. I attempted to use an RPU. for one of the domestic legs, and that's when I was notified by the reservation agent that the fare does not qualify. I knew that going in, because it's clearly denoted when making the reservation and you even check off a box to say that you understand. I tried calling in because there wasn't an upgrade box available when I viewed my ticketed reservation, and per one other poster here they said they had success with reaching an agent and having them manually apply the RPU