Add customer message upon order change to processing based on conditions in WooCommerce

Question

This code works, it adds a note to the order if the customer buys a product which is in a conditional category as well as other products outside of that category and the order is moved to processing. The message is that the customer will receive 2 packages since they ship from different locations. However, I want it to add the message as a customer message rather than a note, but I can't get it to work.

I tried with

    $order->set_customer_note($customer_note);
    $order->save();

but it doesn't work.

My code attempt:

    function add_custom_note_to_order($order_id) {
    $order = wc_get_order( $order_id );

    // Initialize categories array
    $categories = array();

    // Loop through order items
    foreach($order->get_items() as $item) {
        $product_id = $item->get_product_id();
        $terms = get_the_terms($product_id, 'product_cat');
        
        foreach($terms as $term) {
            $categories[] = $term->slug;
        }
    }

    // Categories to check
    $check_categories = array('accessories-1', 'shirtsblue', 'shirtsred', 'shirtsgreen');

    // Check if order contains products from the cat above
    // and also from another category
    if(array_intersect($check_categories, $categories) && sizeof(array_diff($categories, $check_categories)) > 0) {
        $order_note = 'Your order will be shipped in 2 parcels';
        $order->add_order_note($order_note);
    }
}
add_action('woocommerce_order_status_processing', 'add_custom_note_to_order');

Answer 1

When using WC_Order add_order_note() method, there is $is_customer_note 2nd optional argument (boolean), that you need to set it to true, like:

$order_note = 'Your order will be shipped in 2 parcels';

$order->add_order_note($order_note, true);

Now it should work.