“Fatal error: Call to undefined method WooCommerce::add_error() in …………………..

<?php
/**
 * Enqueue the parent theme stylesheet.
 */
add_action( 'wp_enqueue_scripts', 'vantage_parent_style' );
function vantage_parent_style() {
    wp_enqueue_style( 'parent-theme', get_template_directory_uri() . '/style.css' );
}
/**
 * Enqueue the child theme stylesheet.
 */
add_action( 'wp_enqueue_scripts', 'vantage_child_style', 20 );
function vantage_child_style() {
    wp_enqueue_style( 'child-theme', get_stylesheet_uri() );
}
/**
 * Set the child theme text domain.
 */
function vantage_child_set_text_domain(){
load_theme_textdomain( 'vantage', get_stylesheet_directory() . '/languages' );
}
add_action('after_setup_theme', 'vantage_child_set_text_domain', 15);
/**
* Add the field to the checkout
**/
add_action('woocommerce_after_order_notes', 'my_custom_checkout_field');
function my_custom_checkout_field( $checkout ) {
echo '<div id="my_custom_checkout_field"><span>'.__('Personnummer obligatoriskt för fakturering,').'</span>';
woocommerce_form_field( 'my_field_name', array(
'type'          => 'text',
'class'         => array('my-field-class form-row-wide'),
'label'         => __('10 siffror ÅÅMMDD-NNNN'),
'placeholder'       => __('Ditt personnummer, 10 siffror ÅÅMMDD-NNNN'),
), $checkout->get_value( 'my_field_name' ));
echo '</div>';
}
/**
* Process the checkout
**/
add_action('woocommerce_checkout_process', 'my_custom_checkout_field_process');
function my_custom_checkout_field_process() {
global $woocommerce;
// Check if set, if its not set add an error.
if (!$_POST['my_field_name'])
$woocommerce->add_error( __('Please enter something into this new shiny field.') );
}
/**
* Update the order meta with field value
**/
add_action('woocommerce_checkout_update_order_meta', 'my_custom_checkout_field_update_order_meta');
function my_custom_checkout_field_update_order_meta( $order_id ) {
if ($_POST['my_field_name']) update_post_meta( $order_id, 'My Field', esc_attr($_POST['my_field_name']));
}
/*** Add the field to order emails**/add_filter('woocommerce_email_order_meta_keys', 'my_custom_checkout_field_order_meta_keys');function my_custom_checkout_field_order_meta_keys( $keys ) {$keys[] = 'My Field';return $keys;}

Hi,
Do you know how I can change this field setting so its not a mandatory field just a optional field?

Eric

Hi,
Can we pick up this thread were we left of? I haven’t had the time or the courage to try to go into this without some more guidance. I would like to take away the mandatory on this field were costumers can add their social security number.
Can you please guide me witch row I should remove or change?

Eric

Hi Andrew,
Do you mean to my WP media library? Is it not something in the child theme’s functions.php file as mentioned above?

Many thank Adrew & co!
I will try this!

Eric

Hi! I hope you all are fine?! I took courage and time to replace the functions.php file you gave me. But this error message comes:
” Fatal error: Call to undefined method WooCommerce::add_error() in /home/badbanco/public_html/wp-content/themes/vantage-child/functions.php on line 51 “

The function is in the woocomerce checkout page and their is three different payment ways to chose:
First id by a 20 day invoice after delivery, in that case the customers must fill in this extra added field with their social security number. To be able to do a credit check.
The second alternative is prepayment before dispatch and here is should it not me mandatory to enter their social security number. And its here the error message comes the last three month if costumers don’t enter something in the social security number field. Prior that it worked.
The third payment alternative is: Payment in our store with visa or master card on pickup and without something in written in the social security number field the error message comes.