Woocommerce product custom field

I've added a woocommerce product custom field. But I can't access those custom field, like other product attribute through example.com/grocery/wp-json/wc/v2/products.

This is my code,

//Display Fields
add_action( 'woocommerce_product_options_general_product_data', 'woo_add_custom_general_fields' );

//Save Fields
add_action( 'woocommerce_process_product_meta', 'woo_add_custom_general_fields_save' );

function woo_add_custom_general_fields() {

    global $woocommerce, $post;

    echo '<div class="options_group">' ;
             //Purchasing Cost
            woocommerce_wp_text_input(
                array(
                    'id' => '_purchasing_cost',
                    'placeholder' => 'Purchasing Cost',
                    'label' => __('Purchasing Cost', 'woocommerce'),
                    'type' => 'text',                       
                )
            );

             //OverHead
            woocommerce_wp_text_input(

                array(
                    'id' => '_over_head',
                    'placeholder' => 'Overhead',
                    'label' => __('Overhead', 'woocommerce'),
                    'type' => 'text',   

                )
            );  
    echo '</div>';
}

//To Save data
function woo_add_custom_general_fields_save($post_id) {
        //Purchasing Cost
         $woocommerce_purchasing_cost_field = $_POST['_purchasing_cost'];
            if (!empty($woocommerce_purchasing_cost_field))
            update_post_meta($post_id, '_purchasing_cost', esc_attr($woocommerce_purchasing_cost_field));

        //OverHead
         $woocommerce_over_head_field = $_POST['_over_head'];
            if (!empty($woocommerce_over_head_field))
            update_post_meta($post_id, '_over_head', esc_attr($woocommerce_over_head_field));
}