Why is my Shift to Run Script not working? When I press shift, it doesn't do anything!

Hello, fellow helpers! I have a problem... I made a Shift to Run script but it doesn't seem to be working even though it looks fine to me. I've tried to put it in a StarterGUI too, but it doesn't work either.

Here's the LocalScript:

local plr = game.Players.LocalPlayer or game.Players.PlayerAdded:wait()
local char = plr.Character or plr.Character.CharacterAdded:wait()
local humanoid = char.Humanoid
local RunR6 = script.Parent["Run (R6)"]
local RunR15 = script.Parent["Run (R15)"]
local PlayRunR6 = humanoid:LoadCharacter(RunR6)
local PlayRunR15 = humanoid:LoadCharacter(RunR15)
local UserInputService = game:GetService('UserInputService')

UserInputService.InputBegan:connect(function(input)
	if input.KeyCode == Enum.KeyCode.LeftShift then
		if Enum.HumanoidRigType.R6 then
			humanoid.WalkSpeed = 24
			PlayRunR6:Play()
		elseif Enum.HumanoidRigType.R15 then
			humanoid.WalkSpeed = 24
			PlayRunR15:Play()
		end
	end
end)

This checks if you have pressed the Shift key on the left side of keyboard. If it is pressed, it triggers another if statement about detecting what RigType you're avatar is to determine what animation needs to be played (I made an R6 and R15 version of a running animation). When it sees this, it changes the humanoid's (player's) walkspeed to 24 and it plays the animation.

Hierarchy (View)

You could also just use this... Put this in a LocalScript inside of StarterCharacterScripts

-- Locals
local Mouse = game.Players.LocalPlayer:GetMouse()
local char = game.Players.LocalPlayer.Character
local sb = string.byte

-- Main
Mouse.KeyDown:Connect(function(keybyte)
	Key = string.lower(keybyte)
		if sb(keybyte) == 48 then
			char.Humanoid.WalkSpeed = 21
		end
	Mouse.KeyUp:Connect(function(keybyte)
		if sb(keybyte) == 48 then
			char.Humanoid.WalkSpeed = 16
		end
	end)
end)

Try this, if you still have a problem occurring, I'll properly debug it.

Make sure this is in a LocalScript in StarterPack or StarterGui.

local plr = game.Players.LocalPlayer
local char = plr.Character
local humanoid = char:WaitForChild("Humanoid")
local RunR6 = script.Parent["Run (R6)"]
local RunR15 = script.Parent["Run (R15)"]
local PlayRunR6 = humanoid:LoadAnimation(RunR6) -- Notice
local PlayRunR15 = humanoid:LoadAnimation(RunR15) -- Notice
local UserInputService = game:GetService('UserInputService')

UserInputService.InputBegan:connect(function(input)
    if input.KeyCode == Enum.KeyCode.LeftShift then
        if humanoid.RigType == Enum.HumanoidRigType.R6 then
            humanoid.WalkSpeed = 24
            PlayRunR6:Play()
        elseif humanoid.RigType == Enum.HumanoidRigType.R15 then
            humanoid.WalkSpeed = 24
            PlayRunR15:Play()
        end
    end
end)

UserInputService.InputEnded:connect(function(input)
    if input.KeyCode == Enum.KeyCode.LeftShift then
        if humanoid.RigType == Enum.HumanoidRigType.R6 then
            humanoid.WalkSpeed = 16
            PlayRunR6:Play()
        elseif humanoid.RigType == Enum.HumanoidRigType.R15 then
            humanoid.WalkSpeed = 16
            PlayRunR15:Play()
        end
    end
end)