The localscript works in roblox solo mode and not in game/server?

local Player = game.Players.LocalPlayer
local Mouse = Player:GetMouse()
script.PlayerName.Value = game.Players.LocalPlayer.Name
Mouse.KeyDown:connect(function(Key)
	if Key:byte() == 32 then
		if Player.Character.Parent ~= game.Workspace then
			for _, descendant in 	pairs(game.Workspace.FlightModel:GetDescendants())do
				if descendant.Name == script.PlayerName.Value then
					descendant.Parent = game.Workspace
				end
			end
		end
	end 
end)

This is because you scriping doesn't include remoteEvents. RemoteEvents help tranfer data from server to client or client to server. We need to use the Event FireServer. Which will fire your script into the Server which well then be read and be fire into the client aka your game. This allows everyone to see whats going on in game. Here is a youtube video on the fowllowing. if you don't like Remote event you could go into your workspace and turn it off. But if will allow players to hack in your game. Hope i helped :)