Why does my script have "Argument 1 missing or nil?"

This is my script, line 6 is what the output complains about

for i, v in pairs(game.Players:GetPlayers()) do
	if v.TeamColor == BrickColor.new("Bright red") then
		if v:FindFirstChild("PlayerGui") then	
       			v.Character.Humanoid.HealthChanged:connect(function() 
				print("Boss Health Changed")
        			v.PlayerGui.BossHealth.Healthbar.LocalScript.RemoteEvent:FireClient() 
				print('Fired')
 			end)
		end
    end
end

I created this script so that if someone's health from the Bright red team is altered/changed (by use of that HealthChanged function) it is going to fire a remote event to the client. Why is it saying the argument is nil?

Whenever using FireClient, which is used in a Server Script, you need to fill out the first 'argument', or the word in the parenthesis, with the player's name, so that it will fire that specific client. If you're firing all clients, you can ignore the player name, and instead use FireAllClients.

for i, v in pairs(game.Players:GetPlayers()) do
    if v.TeamColor == BrickColor.new("Bright red") then
        if v:FindFirstChild("PlayerGui") then   
                v.Character.Humanoid.HealthChanged:connect(function() 
                print("Boss Health Changed")
                    v.PlayerGui.BossHealth.Healthbar.LocalScript.RemoteEvent:FireClient(v) 
                print('Fired')
            end)
        end
    end
end