PS 1.7 - Make a module hooked on product page returns error or confirmation message

[BeComWeb]

Hi community,

I'm trying to adapt one of my small module for PS 1.7, this one is hooked to the product page (in the "Modules" tab, with "hookDisplayAdminProductsExtra" method)  and i have a question about how to make it returns error or confirmation message (as the ones that appear on the top-right corner when updating a product).

Currently the module is correctly showing in the tab and the data are sent to the module when clicking "Save".

But i don't understand how to pass an error or confirmation message to the product page.

Here is my code :

    public function hookActionProductUpdate($params)
    {
        $cpcd_array = Tools::getValue("cpcd");
        $new_product_date = $cpcd_array['changeproductcreationdate']['product_creation_date'];
        if (!Validate::isDate($new_product_date)) {
            //die('invalid date'); //showing in the console
            return $this->displayError($this->l('Invalid date')); //not working
        }
    }

Does anybody has an idea on how to perform this ?