The GUI button does not appear for a specific player, outdated method?

countdown = 11

username = "AntonioVillavicencio"
if game.Players.LocalPlayer.Name == username then
	script.Parent.launch.Visible = true
end

script.Parent.launch.MouseButton1Click:connect(function()
	
	while countdown > 0 do
		countdown = countdown - 1
		script.Parent.COUNT.Text = countdown
		wait(1)
	end
	
	script.Parent.COUNT.Text = "WE HAVE LIFT-OFF"
	
	game.ReplicatedStorage:WaitForChild("workspaceEvents").rockets.launch:FireServer()
end)

why does the following segment not work :

username = "AntonioVillavicencio"
if game.Players.LocalPlayer.Name == username then
	script.Parent.launch.Visible = true
end

Ingame, the button does not appear. The rest of the script works smoothly.

Here, try this instead. I recommend you put this in a LocalScript because a Server Script cannot read "LocalPlayer".

That could have been your problem if you're using a normal Script. USE LocalScript on Client Side if you're going to refer to it as the Local Player.

-- AntonioVillavicencio

local ReplicatedStorage = game:GetService('ReplicatedStorage')
local Player = game.Players.LocalPlayer

local CountDown = 11
local User = game.CreatorId

if Player.UserId == User then
	script.Parent.launch.Visible = true
end

script.Parent.launch.MouseButton1Down:Connect(function()
	while wait(1) and CountDown > 0 do
		CountDown = CountDown - 1
		script.Parent.COUNT.Text = CountDown
	end
	script.Parent.COUNT.Text = 'WE HAVE LIFT-OFF'
	ReplicatedStorage:WaitForChild("workspaceEvents").rockets.launch:FireServer()
end)

If you wanna add in extra info, replace all of line 16 with the following code;

if script.Parent.COUNT.Text > 1 then
	script.Parent.COUNT.Text = CountDown .. ' seconds until lift-off.'
elseif script.Parent.Count.Text == 1 then
	script.Parent.COUNT.Text = CountDown .. 'second until lift-off.'
end

Lolll