Debug prints but other player's gui doesn't open?

I'm trying to make it to where when a player clicks on another player a gui opens on their screen. I have this as a local script:

local Player = game.Players.LocalPlayer -- Getting the player   
local Mouse = Player:GetMouse() -- Getting the players mouse


Mouse.Button1Down:Connect(function() -- Detecting when player presses the left mouse button
	
    if Mouse.Target.Parent:FindFirstChild("Humanoid") and 
        game.Players.LocalPlayer.TeamColor.Name == ("Dirt brown") then -- Checking if the Mouse is over a player
        print(Mouse.Target.Parent.Name) 
	local mousetarget = Mouse.Target.Parent
		game.ReplicatedStorage.SellPistol:FireServer(mousetarget)
		
	


    end
end)

Someone told me to use get player on the script this connects to under ServerScriptService:

local SellPistol = game.ReplicatedStorage.SellPistol

local function onSellPistol(player, mousetarget)
    local target = game:GetService("Players")[mousetarget.Name]
    target.PlayerGui.StartScreen.Frame.Visible = true
    print("Debug")
end

SellPistol.OnServerEvent:Connect(onSellPistol)

now the debug prints but the gui doesn't open why?