Walking sounds script not working in game how do i fix this?

-- Client Script
-- Place into StarterCharacterScripts as Local Script

local Players = game:GetService("Players") -- Player Service
local LocalPlayer = Players.LocalPlayer -- Local Player
local Character = LocalPlayer.Character or LocalPlayer.CharacterAdded:Wait() -- Local Player's character

repeat wait() until Character and game:IsLoaded() -- Once everything is loaded properly.

local Humanoid = Character.Humanoid -- Our humanoid to retrieve our FloorMaterial property
local HumanoidRootPart = Character.HumanoidRootPart -- Character HRP

local RunningSound = HumanoidRootPart.Running -- Our running sound.

local OldSoundID, OldSoundVol -- We'll need these if the material type doesn't match
OldSoundID = RunningSound.SoundId
OldSoundVol = RunningSound.Volume

local MaterialTypes = { -- Our material types.
['Glass'] = Enum.Material.Glass;
['Sand'] = Enum.Material.Sand;
['Wood'] = Enum.Material.Wood;
['Rock'] = Enum.Material.Rock;
}

local CheckIfMaterial = function(Material)
	if Humanoid.FloorMaterial == Material then
		return true
	end
	return false
end

--[[ CheckIfMateiral Function
 Argument[1] - Material Input
 Returns true/false depending if the FloorMaterial
 is valid to the arguement given.	
]]

Humanoid:GetPropertyChangedSignal('FloorMaterial'):Connect(function() -- Our event to check if FloorMaterial gets changed
  if CheckIfMaterial(MaterialTypes.Glass) or CheckIfMaterial(MaterialTypes.Sand) then -- Checking if Glass or Sand for FloorMaterial
     RunningSound.SoundId = "rbxassetid://510933218" -- Sets to ID 
     RunningSound.Volume = 1 -- Volume set
  elseif CheckIfMaterial(MaterialTypes.Wood) or CheckIfMaterial(MaterialTypes.Rock) then -- Same as above 
     RunningSound.SoundId = "rbxassetid://2991635108"
     RunningSound.Volume = .1
	else -- If not's matching anything of the above we set to normal walking sound. Optional, you can remove this but i thought you needed it anyways.
     RunningSound.SoundId = OldSoundID
     RunningSound.Volume = OldSoundVol
    end
end)

I've tested this and works perfectly according to what you needed to be fixed and what you wanted. Keep notes of this code and remember that there's events for the Humanoid which can make your process 10x easier and far more efficient. See you around, have a nice day.

Although i'm sorry this could've been much more simplified but i was bored and tired at the time, might update it later.