ContextActionService:GetButton() not working?

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Hello, im trying to resize and position the button that ContextActionService made for the Slash Button, but it returns this error in the output.

Error:

13:14:08.380 Workspace.PlayerName.LocalScript:45: attempt to index nil with ‘Size’ - Client - LocalScript:45
13:14:08.381 Stack Begin - Studio
13:14:08.381 Script ‘Workspace.PlayerName.LocalScript’, Line 45 - Studio - LocalScript:45
13:14:08.381 Stack End

Script:

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local CAS = game:GetService("ContextActionService")

local player = game.Players.LocalPlayer
local character = script.Parent
local humanoid = character:WaitForChild("Humanoid")

local Backpack = player:WaitForChild("Backpack")
local Tool = Backpack:WaitForChild("ClassicSword")

local animation = ReplicatedStorage.Animations:WaitForChild("Slash")
local slashTrack = humanoid.Animator:LoadAnimation(animation)

local debounce = false

local function playAnimation()
	debounce = true
	slashTrack:Play()

	humanoid:EquipTool(Tool)
	
	slashTrack.Ended:Connect(function()
		humanoid:UnequipTools(Tool)
	end)
	
	task.delay(35, function()
		debounce = false
	end)
end

local function onSlash(actionName, inputState)
	if actionName == "Slash" and inputState == Enum.UserInputState.End and not debounce then
		playAnimation()
	end
end

if debounce then
	CAS:UnbindAction("Slash")
elseif not debounce then
	CAS:BindAction("Slash", onSlash, true, Enum.KeyCode.Q)
end

local slashButton = CAS:GetButton("Slash")

slashButton.Size = UDim2.new(50, 50, 0, 0)
slashButton.Position = UDim2.new(50, 50, 0, 0)

Does anyone know what’s happening?