您正在寻找的挂钩是“woocommerce payment complete”，一旦订单标记为“complete”，就会触发该挂钩。在该钩子调用的函数中，您需要获取应用于订单的所有优惠券，并检查其中是否有您正在寻找的优惠券。

add_action( \'woocommerce_payment_complete\', \'so_payment_complete\' );
function so_payment_complete( $order_id ){

        // Get an instance of WC_Order object
        $order = wc_get_order( $order_id );

        // Coupons used in the order LOOP (as they can be multiple)
        foreach( $order->get_used_coupons() as $coupon_code ){

            // Retrieving the coupon ID
            $coupon_post_obj = get_page_by_title($coupon_code, OBJECT, \'shop_coupon\');
            $coupon_id       = $coupon_post_obj->ID;

            // Get an instance of WC_Coupon object in an array(necessary to use WC_Coupon methods)
            $coupon = new WC_Coupon($coupon_id);
            $coupon_code = $coupon->get_code();

            // Check if it\'s the right coupon
            if ( $coupon_code == \'mycoupon\' ){

                $to = "[email protected]";
                $subject = "Coupon $coupon_code has been applied";
                $content = "
                The coupon code $coupon_code has been applied by a customer
                ";

                wp_mail( $to, $subject, $content );

            }

        }
}