Put your operating system (Windows 7, Windows XP, OSX) and Java version if you know it here
The /replaceitem command is buggy.
*What I expected to happen was the Elytra to be placed in my armor slot.
*What actually happened: after setting the command,
the command block gave me an error message.
PS. the command still works in other slots
Steps to Reproduce:
1. Place a command block down an put in the following command.
2. /replaceitem entity [name] slot.armor.chest minecraft:elytra 1 0
3. Activate it (I've already tried all the different ways)