GUI: PlayerGui is not a valid member of Player?

To mention in this case there are 2 persons involved, the “staff” and the “customer”, the customer is signaled by a textbox and the staff is the local plr.

In this case, I have 2 scripts one local and a normal script, in this case the error is with the local script which activates the process with a RemoteEvent. I already tried to add a value to PlayerGui with:

local PlayerGui = Target:FindFirstChild("PlayerGui")
local PlayerGui = Target:WaitForChild("PlayerGui")

But nothing happens... Here are the script:

LOCAL SCRIPT:

MCI.Prompt.OnClientEvent:Connect(function(Target, command)
    if command == "CustomerHandler" then
        local Text = script.Parent.System.Player.Text
        local Target = game:GetService("Players"):FindFirstChild(Text) 
        Target.PlayerGui.MCICustomerPromptHandler:TweenPosition(UDim2.new(0.29, 0,0.014, 0))
        print("Sent customer handler")
    end
end)

SERVER SCRIPT:

script.Parent.Parent.StaffPromptHandler.Purchase.MouseButton1Click:Connect(function()
    script.Parent.Parent.StaffPromptHandler:TweenPosition(UDim2.new(0.29, 0,-1.014, 0))
    wait(.5)
    MCI.Prompt:FireAllClients(Target,"CustomerHandler")
    print("sent command customer handler for:" .. Target.Name)
end)