My mouse cursor icon won't change, anyone know how to do it correctly?

This is my script that changes the mouse cursor icon:

mouse.Icon = "rbxassetid://166736756"

The problem is, it doesn't change the mouse icon. Do anyone knows how to change the cursor icon correctly?

It's a localscript, so yeah.

Here's my full script:

--[[
	Made by TheRobloxPlayer2509
    Private gun script
--]]

repeat wait()
until script.Parent.Parent.Parent:IsA("Player") or script.Parent.Parent.Parent:IsA("Model")
--Defines
local tool = script.Parent
local config = tool.Configuration
local clip = config.ClipSize
local unlimited = config.Unlimited
local reserve = config.Remain
local remote = tool:WaitForChild("RemoteEvent")
local plr = game.Players.LocalPlayer
local mouse = plr:GetMouse()
local gungui = script.GunGui
local aimgui = script.AimGui
local anim = {} -- A table that holds all animations

--Variables
local ammo = clip.Value
local debounce = true
local cooldown = 0.15 -- In second
local equipped = false
local range = 300 -- By stud
local holding = false
local spread = 5 -- Better keep this low, the spread will be higher depends on the distance
local aiming = false -- If it's aiming, the spread will decrease by half
local aimFOV = 50 -- The field of view when aiming, default is 70

local currentspread = spread -- ignore this

--Advanced Settings
local ignoreWater = true -- Makes bullet shoot through water
local gridifyTerrainCells = false -- Just make this false

--Functions
local function decode(kind, code)
	if kind == "byte" then
		local success, msg = pcall(function()
			string.byte(code)
		end)
		if not success then
			warn(msg)
			return nil
		end
		if success then
			return string.byte(code)
		end
	end
end

local function aim()
	local cam = game.Workspace.CurrentCamera
	cam.FieldOfView = 70
	game.Players.LocalPlayer.CameraMode = Enum.CameraMode.LockFirstPerson
	local minusFOV = 70 - aimFOV
	aimgui.Parent = plr.PlayerGui
	for i,v in pairs(tool:GetChildren()) do
		if v.Name ~= "Fire" then
			if v:IsA("UnionOperation") then
		        v.Transparency = 1
		    end
		end
	end
	for i = 1,minusFOV do
		cam.FieldOfView = cam.FieldOfView - 1
		wait(0.01)
	end
	cam.FieldOfView = aimFOV
end

local function unaim()
	local cam = game.Workspace.CurrentCamera
	cam.FieldOfView = aimFOV
	game.Players.LocalPlayer.CameraMode = Enum.CameraMode.Classic
	local plusFOV = 70 - aimFOV
	aimgui.Parent = script
	for i,v in pairs(tool:GetChildren()) do
		if v.Name ~= "Fire" then
			if v:IsA("UnionOperation") then
		        v.Transparency = 0
		    end
		end
	end
	for i = 1,plusFOV do
		cam.FieldOfView = cam.FieldOfView + 1
		wait(0.01)
	end
	cam.FieldOfView = 70
end

tool.Equipped:Connect(function()
	equipped = true
	aiming = false
	aimgui.Parent = script
	gungui.Parent = plr.PlayerGui
	anim[1] = game.Players.LocalPlayer.Character.Humanoid:LoadAnimation(script.Idle)
	game.Workspace.CurrentCamera.FieldOfView = 70
	mouse.Icon = "rbxassetid://166736756"
	wait(0.5)
	anim[1]:Play()
end)

tool.Unequipped:Connect(function()
	equipped = false
	aiming = false
	aimgui.Parent = script
	gungui.Parent = script
	anim[1]:Stop()
	mouse.Icon = ""
	game.Workspace.CurrentCamera.FieldOfView = 70
end)

mouse.Button1Down:Connect(function()
	holding = true
end)

mouse.Button1Up:Connect(function()
	holding = false
end)

mouse.Button2Down:Connect(function()
	if equipped == true then
		aiming = true
		aim()
	end
end)

mouse.Button2Up:Connect(function()
	if equipped == true then
		aiming = false
		unaim()
	end
end)

mouse.KeyDown:Connect(function(key)
	local code = decode("byte", key)
	if code ~= nil then
		if equipped == true then
		    if code == 114 then
			    if config.AmmoInClip.Value < config.ClipSize.Value then
				    if config.Remain.Value > 0 then
				        remote:FireServer("reload")
				        equipped = false
				        wait(4) -- The reload time
				        if script.Parent.Parent:IsA("Model") then
				            equipped = true
				       else equipped = false
				    end
				    elseif config.Unlimited.Value == true then
				    	remote:FireServer("reload")
				        equipped = false
				        wait(4) -- The reload time			    
				        if script.Parent.Parent:IsA("Model") then
				        equipped = true
				    else equipped = false
					    end
				    end
				end
			end
		end
	end
end)

while wait(cooldown) do
	if equipped == true then
		if holding == true then
			local realSpread = spread
			if config.AmmoInClip.Value > 0 then
				if (mouse.hit.p - tool.Fire.Position).magnitude > 100 and (mouse.hit.p - tool.Fire.Position).magnitude <= 250 then
					realSpread = spread * 2
				end
				if (mouse.hit.p - tool.Fire.Position).magnitude > 250 and (mouse.hit.p - tool.Fire.Position).magnitude <= 500 then
					realSpread = spread * 4
				end
				if (mouse.hit.p - tool.Fire.Position).magnitude > 500 and (mouse.hit.p - tool.Fire.Position).magnitude <= 1000 then
					realSpread = spread * 6
				end
				if (mouse.hit.p - tool.Fire.Position).magnitude > 1000 and (mouse.hit.p - tool.Fire.Position).magnitude <= 2500 then
					realSpread = spread * 8
				end
				if (mouse.hit.p - tool.Fire.Position).magnitude > 2500 then
					realSpread = spread * 10
				end
			    if aiming == true then
			    	realSpread = spread / 2
			    end
			    remote:FireServer("fire", mouse.Hit.p, realSpread)
			    print("firing")
			else tool.Fire.Click:Play()
			end
		end
	end
end