Copied code from roblox guide and doesn't work?

Just copied the code and everything from this guide https://developer.roblox.com/en-us/articles/Double-Jumping

It just doesnt work at all. I have no idea whats wrong, but literally nothing happens. im new to dev in roblox so some help would be nice. thanks

if it helps this is the code:

local UserInputService = game:GetService("UserInputService")
local localPlayer = game.Players.LocalPlayer
local character
local humanoid

local canDoubleJump = false
local hasDoubleJumped = false
local oldPower
local TIME_BETWEEN_JUMPS = 0.2
local DOUBLE_JUMP_POWER_MULTIPLIER = 2

function onJumpRequest()
    if not character or not humanoid or not character:IsDescendantOf(workspace) or
     humanoid:GetState() == Enum.HumanoidStateType.Dead then
        return
    end

    if canDoubleJump and not hasDoubleJumped then
        hasDoubleJumped = true
        humanoid.JumpPower = oldPower * DOUBLE_JUMP_POWER_MULTIPLIER
        humanoid:ChangeState(Enum.HumanoidStateType.Jumping)
    end
end

local function characterAdded(newCharacter)
    character = newCharacter
    humanoid = newCharacter:WaitForChild("Humanoid")
    hasDoubleJumped = false
    canDoubleJump = false
    oldPower = humanoid.JumpPower

    humanoid.StateChanged:connect(function(old, new)
        if new == Enum.HumanoidStateType.Landed then
            canDoubleJump = false
            hasDoubleJumped = false
            humanoid.JumpPower = oldPower
        elseif new == Enum.HumanoidStateType.Freefall then
            wait(TIME_BETWEEN_JUMPS)
            canDoubleJump = true
        end
    end)
end

if localPlayer.Character then
    characterAdded(localPlayer.Character)
end

localPlayer.CharacterAdded:connect(characterAdded)
UserInputService.JumpRequest:connect(onJumpRequest