Why does my coins saving system not save?

It's a really messy code.

1. Update your script

2. PlayerRemoving and disconnecting are okay, but shouldn't be your only saves

3. It's UserId, not userId --> edit, this would have worked and it might still, but it's deprecated

4. Use pcall!

5. Use WaitForChild

6. The second param of instance.new is also deprecated (parent)!

DataStore = game:GetService("DataStoreService"):GetDataStore("Coins")

game.Players.PlayerAdded:Connect(function(Player)
	local Key = "user_" .. Player.UserId
	local x = Instance.new("NumberValue")
	x.Name = "Coins"
	x.Value = DataStore:GetAsync(Key) or 0
	x.Parent = Player
end)

while wait(10) do
	local success, message = pcall(function()
		for index, plr in pairs(game.Players:GetPlayers()) do
			local Key = "user_" .. plr.UserId
  			DataStore:SetAsync(Key, plr:WaitForChild('Coins').Value)
		end
	end)

	if not success then
		print('warning, datastore error: '..message)
	end
end

If this still doesn't work, there can be a few causes

1. You're in studio and you don't have API access enabled

2. I made a typo

3. Coins doesn't exist

4. Something else

Also, I added 'or 0' because it might never have saved before! (and it's easier than checking if it's nil

If you still see any error or it doesn't work, just ask :)