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