Troubleshooting: InterestItemAdd returns no response when invalid parameters are received

There is a limitation when calling the InterestItemAdd command using AJAX calls in the storefront, for example, AjaxInterestItemAdd.

If the updateable attribute is set to 0, an error message is not displayed when a customer attempts to add a wish list item that already exists in the wish list.

To avoid this issue:
  1. The default behavior should be kept, where no error message is shown when a repeated item is added to the wish list.

It is treated as a successful addition to the wish list, although the item already exists in the customer's wish list.