Script Will Not Add Frame To Gui After Getting New Item Inside Inventory Folder?

This is a normal script running after a remote function is fired.

local AddItem = game:GetService("ReplicatedStorage").Events.AddItem

function UpdateQuantity(ItemName,Amount)
    script.Parent.Background.Holder[ItemName].ItemQuantity.Text = "x"..Amount
end

function AddItem.OnServerInvoke(player,ItemName,Quantity)
    if script.Parent.Inventory:FindFirstChild(ItemName) then
        script.Parent.Inventory[ItemName].Quantity.Value = script.Parent.Inventory[ItemName].Quantity.Value + Quantity
UpdateQuantity(ItemName,script.Parent.Inventory[ItemName].Quantity.Value)
        return
    end
    local Item = Instance.new("Folder")
    Item.Name = ItemName
    local Quantityy = Instance.new("NumberValue")
    Quantityy.Name = "Quantity"
    Quantityy.Value = Quantity
    Item.Parent = script.Parent.Inventory
    Quantityy.Parent = Item
end

It doesn't print any errors. It adds the frame in roblox studio but not in game.