Show error message when trying to add more items than available to cart

[LuiPru]

I am looking for a solution to display an error message in the cart when trying to add more items than are available/in stock. On the product itself it shows an error, but not when trying to change the quantity in the cart.

Currently it looks like a bug to the users, because it's not visible to them what exactly is going on.

Does anyone know a solution for this? I am looking for a small error message like "You cannot add more items, because we don't have more."

The shop is www.cdc-reitsport.com and you can find a small screenvideo here: https://drive.google.com/file/d/1KNeGUJWdBFBgawPwZWwK6TqQHR_7Mj7X