Trying to learn Filtering Enabled, need some help with this?

I just started to learn filtering enabled, and the idea is to create a part in the server when the player presses a key.It works for me in Studio but when I Start a server in studio to see if it actually works with FE on it doesn't work anymore

--This is in a local script.
Player = game:GetService("Players").LocalPlayer
Char = Player.Character
mouse = Player:GetMouse()

mouse.KeyDown:connect(function(key)
    if key == "j" then
        script.Test.JustTesting:FireServer()
    end
end)

--This is a script inside the local script 
Player = game:GetService("Players").LocalPlayer
Char = Player.Character
--JustTesting is a remote event inside the script
script.JustTesting.OnServerEvent:connect(function()
        a = Instance.new("Part", workspace)
        a.CFrame = Char.Torso.CFrame*CFrame.new(0, 0, -10)
end)

Thank you!