Mineplex lets you join with versions 1.8 to 1.14. However, because it allows you to join with 1.8, a very old version, you cannot use anything added in 1.9+. In the game, Master Builders, players cannot place any of the newer blocks because of Mineplex using 1.8. I am confused on why Mineplex is using a version from 5 years ago. I believe it is time to update.