If the sendChat does work, your event handler doesn't have any parameters to "receive" any events and the if/elseif checks will always fail.
Code:
function FSMB:OnEvent(event, ...)
local arg1, arg2, arg3 = ...
You might want to look into C_ChatInfo.SendAddonMessage as I think the prefix is supposed to be the first parameter and I'm not sure the others are correct.