How do i make this tween in servers?

The tweening part of this script works perfectly in studio and studio server test but not in the actual game. Everything else works perfectly except the tweening. All i need help with is making the tween work in servers.

local NPC = script.Parent.UpperTorso

while true do
	local ply = game.Players:GetChildren()
	for i = 1, #ply do 
		local char = game.Workspace:findFirstChild(ply[i].Name) 
		if char ~= nil then 
			if (NPC.Position - char.UpperTorso.Position).magnitude <= 8 then 
                if ply[i]:findFirstChild("TalkingToNPC") then 
               else
	            if ply[i].Gamestuff.Characters.Folder.Class.Value == "None" then
		        local thing = Instance.new("StringValue",ply[i])
	            thing.Name = "TalkingToNPC"
	                 local ChatClone = script.ChatGui:Clone()
	                 ChatClone.Name = "ChatClone"
	                  ChatClone.Parent = ply[i].PlayerGui
	                   ChatClone.Press:TweenPosition(UDim2.new(0.5, -150, 1, -200), "Out", "Back", 0.7, false)
	                   ChatClone.KeyPress.Disabled = false
	             elseif ply[i].Gamestuff.Characters.Folder.Class.Value ~= "None" then
	           	local thing = Instance.new("StringValue",ply[i])
	            thing.Name = "TalkingToNPC"
	                local ChatClone = script.ChatGui2:Clone()
	                  ChatClone.Name = "ChatClone"
	                  ChatClone.Parent = ply[i].PlayerGui
	                 ChatClone.Press:TweenPosition(UDim2.new(0.5, -150, 1, -200), "Out", "Back", 0.7, false)
	                 ChatClone.KeyPress.Disabled = false
		         end
                end

			elseif (NPC.Position - char.UpperTorso.Position).magnitude > 8 then 
				if ply[i].PlayerGui:findFirstChild("ChatGui") or ply[i].PlayerGui:findFirstChild("ChatGui2") or  ply[i].PlayerGui:findFirstChild("ChatClone") then --:findFirstChild("TalkingToNPC")
			ply[i]:findFirstChild("TalkingToNPC"):destroy()
			ply[i].PlayerGui.ChatClone.Press:TweenPosition(UDim2.new(0.5, -150, 1.5, -200), "In", "Back", 0.7, true)
			wait(0.8)
			ply[i].PlayerGui.ChatClone:destroy()
			   end
				wait()
			end 
		end 
	end
	wait(0.1)
end

The reason your code works in Roblox Studio is because both server scripts and local scripts are the same when you click on the Play button inside roblox studio. When you wish to test if your game works, use the Start button under Clients and Servers .

Server scripts can't access the PlayerGui.

You'll have to use remote events for that.

If you need an example onto that, I'll gladly help you.