Add a custom order note programmatically in Woocommerce admin order edit pages

From a dynamic Order Id you can use WC_Order add_order_note() method this way:

// If you don't have the WC_Order object (from a dynamic $order_id)$order = wc_get_order(  $order_id );// The text for the note$note = __("This is my note's text…");// Add the note$order->add_order_note( $note );

Tested and works.

Thank you guys I was trying to find a way to add the notes to a new order. I was looking for the right hook using the solution that @LoicTheAztec posted. This is the solution that worked for me hope it helps someone else out there.

add this to the Functions.php file

add_action( 'woocommerce_new_order', 'add_engraving_notes',  1, 1  );function add_engraving_notes( $order_id ) { //note this line is different  //because I already have the ID from the hook I am using. $order = new WC_Order( $order_id );  // The text for the note $note = __("Custom Order Note Here"); // Add the note $order->add_order_note( $note );}

This code will do trick for you add code in functions.php

<?phpadd_action('woocommerce_after_order_notes', 'customise_checkout_field');function customise_checkout_field($checkout){    echo '<div id="customise_checkout_field"><h2>' . __('Heading') . '</h2>';    woocommerce_form_field('customised_field_name', array(        'type' => 'text',        'class' => array(        'my-field-class form-row-wide'    ) ,    'label' => __('Customise Additional Field') ,    'placeholder' => __('Guidence') ,    'required' => true,    ) , $checkout->get_value('customised_field_name'));    echo '</div>';}

For data validation of the custom field use the code given below:

add_action('woocommerce_checkout_process', 'customise_checkout_field_process'); function customise_checkout_field_process(){    // if the field is set, if not then show an error message.    if (!$_POST['customised_field_name']) wc_add_notice(__('Please enter value.') , 'error');}

Update value of field

add_action('woocommerce_checkout_update_order_meta', 'customise_checkout_field_update_order_meta');                     function customise_checkout_field_update_order_meta($order_id){    if (!empty($_POST['customised_field_name'])) {        update_post_meta($order_id, 'Some Field', sanitize_text_field($_POST['customised_field_name']));    }}