Attempt to index global 'key' (a nil value)?

I'm trying to make a weapon that plays an animation when you press the R key.

15:45:56.829 - Players.Player.Backpack.Tool.Laser:47: attempt to index global 'key' (a nil value)

How would I fix this?

local tool = script.Parent
local player = game:GetService("Players").LocalPlayer
 
tool.Equipped:connect(function(mouse)
	mouse.Button1Down:connect(function()
	down = true;
	while down do

		local ray = Ray.new(tool.Red.CFrame.p, (mouse.Hit.p - tool.Red.CFrame.p).unit * 300)
		local part, position = workspace:FindPartOnRay(ray, player.Character, false, true)
 
		local beam = Instance.new("Part", workspace)
		beam.BrickColor = BrickColor.new("Really red")
		beam.FormFactor = "Custom"
		beam.Material = "Neon"
		beam.Transparency = 0.25
		beam.Anchored = true
		beam.Locked = true
		beam.CanCollide = false
 
		local distance = (tool.Handle.CFrame.p - position).magnitude
		beam.Size = Vector3.new(0.3, 0.3, distance)
		beam.CFrame = CFrame.new(tool.Red.CFrame.p, position) * CFrame.new(0, 0, -distance / 2)
 
		game:GetService("Debris"):AddItem(beam, 0.1)
 
		if part then
			local humanoid = part.Parent:FindFirstChild("Humanoid")
 
			if not humanoid then
				humanoid = part.Parent.Parent:FindFirstChild("Humanoid")
			end
 
			if humanoid then
				humanoid:TakeDamage(0)
			end
		end
		wait();
end;
end);
	
	mouse.Button1Up:connect(function()
down = false;
end);
end)

key.KeyDown:connect(function(h)
if h=="R" then print("lol this is a test") end 
end)

KeyDown is deprecated, use UserInputService.

local uis=game:GetService("UserInputService")

uis.InputBegan:connect(function(key)
	if key.KeyCode==Enum.KeyCode.R then --really no need for lower
		print'User pressed R!'
	end
end)

Ik this was 4 years ago but ima still answer, make a variable for Mouse

game.Players.PlayedAdded:Connect(function(Player)
local mouse = Player:GetMouse()
mouse.KeyDown:connect(function(h)
if h == "r" then
print("lol this is a test")
end
end)

this should work