Inventory Store Error (Attempt to get length of upvalue) Whats Wrong?

13:05:55.555 - ServerScriptService.Inventory:15: attempt to get length of upvalue 'inv' (a userdata value) 13:05:55.556 - Stack Begin 13:05:55.557 - Script 'ServerScriptService.Inventory', Line 15 13:05:55.558 - Stack End

Output ^^^^

local inv = game:GetService("DataStoreService"):GetDataStore('InventoryMetricDevGalacticzy')

game.Players.PlayerAdded:Connect(function(plr)
	local inventory = Instance.new("Folder",plr)
	inventory.Name = 'Inventory'
	local items = inv:GetAsync(plr.UserId) or {}
	for i,v in pairs(items) do
		if game.ReplicatedStorage.ItemValues:FindFirstChild(v) ~= nil then
			game.ReplicatedStorage.ItemValues[v]:Clone().Parent = inventory
		end
	end
	inventory.ChildAdded:connect(function(c)
		inv[#inv+1] = c.Name -- error here
		inv:SetAsync(plr.UserId, inv)
	end)
	inventory.ChildRemoved:connect(function(c)
		local items = {}
		for i,v in pairs(inventory:GetChildren()) do
			items[i] = v.Name
		end
		inv:SetAsync(plr.UserId, items)
	end)
end)

Script^^^

Please help it is for my game I just need a quick fix and that is all thanks :D

Line 13 of this extract:

inv[#inv+1] = c.Name

You're calling the length operator on a datastore, which you can't do

I'm guessing what you meant to do was:

items[#items+1] = c.Name
inv:SetAsync(plr.UserId, items)