J. A Poetz Druggist What Is The Difference Between J Class And D Class On Virgin Atlantic Flights?

What is the difference between J class and D class on Virgin Atlantic flights? - j. a poetz druggist

Curious, because he already paid a lot for the D-class ticket, but was told he would have to pay more to move the deadline, since only J-class seats for the new date. Make get-class J to something that the D?