This is from the Lodestone stite
/partycmd(/pcmd) [subcommand] Executes various party commands.
add - Invite targeted PC to your party.
leave - Leave your current party.
oust [name] - Oust a PC from your party.
disband - Dissolve your current party.
/join - Accepts a party invite.
/decline - Declines a party invite.
Maybe try  around the target instead of <> ? Thats all I can suggest