Using the command /replaceitem entity @p slot.armor.<slotname> <item> will place the item in the wrong slot.
.head (slot 101): Error message
.chest (slot 100): Error message
.legs (slot 99): Offhand
.feet (slot 98): Main hand
MC-83041
Armor slots in /replaceitem do not work as intended
Resolved
Fixed
2
Can confirm.
The slot.armor slots seem to all target the slot 2 numbers lower than what they should. Thus, you can replace boots with slot.armor.chest slot, leggings with slot.armor.head, mainhand with slot.armor.feet, and offhand with slot.armor.legs.