This rate concerns all the wrong products that you send out and should, therefore, always be zero. It is imperative to send the product that the customer has ordered.
If, for example, the customer orders 32GB product but you have only 16GB version, then do not send the product without saying anything. Instead, it is better to inform the customer of the discrepancy or to cancel the order within a 24-hour period at the minimum. Nevertheless, with an accurate update of your stock level, this eventuality should not take place.