Remote Event Firing Error - How do we fix it?

Im trying to send a remote event to open a gui and whenever the game opens this error pops up..

-- script
local event = game.ReplicatedStorage:WaitForChild("TriggerSignPopUp")

event.OnClientEvent:Connect(function(player)
	player.PlayerGui.CoronaVirusFrontController.Enabled = true
end)

The Error:

-- error
 - OnClientEvent can only be used on the client
 - Stack Begin
 - Script 'ServerScriptService.Script', Line 3
 - Stack End

And here's the script that's firing it:

-- local script

local clickdetector = script.Parent:WaitForChild("ClickDetector")
local event = game.ReplicatedStorage:WaitForChild("TriggerSignPopUp")
local player = game.Players.LocalPlayer
local groupid = 8333540
local cd = false

clickdetector.MouseClick:Connect(function()
	if player:GetRankInGroup(groupid) >= 5 and not cd then
		event:FireClient(player)
		cd = true
		wait(4)
		cd = false
	elseif cd then
		print("on cooldown")
	end
end)