WooCommerce Germanized Pro 2.1.6 - send packing slip via email

functions.php

/*
 * WooCommerce Germanized Pro 2.1.6
 * Function to send packing slip via email
 **/
function woocommerce_order_status_processing_callback($order_id) {

    if ( ! $order_id ) {
        return;
    }

	$order = new WC_Order( $order_id );

	if ( function_exists( 'wc_gzd_get_shipments_by_order' ) ) {
		$shipments = wc_gzd_get_shipments_by_order( $order );
		
		if ( ! empty( $shipments ) ) {
			// Use first shipment as fallback
			$shipment = $shipments[0];
		} else {
			return false;
		}
		
		if ( $packing_slip = wc_gzdp_get_packing_slip_by_shipment( $shipment ) ) {
		
			$to = 'user@example.com';
			$headers = array();
			$headers[] = 'From: Shop <shop@example.de>';
			$attachments = array( $packing_slip->get_pdf_path() );
			wp_mail( $to, 'Lieferschein zur Bestellung: '.$order->get_order_number.'', 'Der Lieferschein befindet sich im Anhang.', $headers, $attachments );
		
		}	

		// add order note
		$note = 'Der Lieferscheint wurde an ' . $to . ' gesendet.';
		$order->add_order_note( $note );

	}
	
}
add_action( 'woocommerce_order_status_processing', 'woocommerce_order_status_processing_callback');