You are trying to SEND a hosttarget to chat?
Twitch sends HOSTTARGETs as a specicial message (like how a regular message is of type PRIVMSG)
You cannot send a HOSTTARGET, twitch sends a HOSTTARGET
If you want to send a host to change the host on a given channel you just send .host TARGETCHANNEL to the channel you want to change the host of.
So if I want to use my bot to change hosts on my channel to cohhcarnage
BarryCarlyonBot would send a PRIVMSG of .host cohhcarnage to the channel barrycarlyon