//Woo API
function api_additonal_data( $shipment_data, $order_id, $shipment_number ){
//Note: Please use the meta key you have set in the custom fields addon
    $shipment_data['_wpcwp2p_order_data'] = array(
        '_date_created'         => wc_format_datetime( $order->get_date_created(), get_option( 'date_format' ) . ' ' . get_option( 'time_format' ) ),
        '_payment_method'       => $order->get_payment_method_title(),
        '_payment_subtotal'     => $order->get_subtotal_to_display(),
        '_payment_total'        => $order->get_formatted_order_total(),
        '_total_tax'            => wc_price( $order->get_total_tax(), array( 'currency' => $order->get_currency() ) ),
        '_total_discount'       => wc_price( $order->get_total_discount(), array( 'currency' => $order->get_currency() ) ),
        '_shipping_tax'         => wc_price( $order->get_shipping_tax(), array( 'currency' => $order->get_currency() ) ),
        '_shipping_total'       => wc_price( $order->get_shipping_total(), array( 'currency' => $order->get_currency() ) ),
        '_payment_items_fee'    => $items_fee,
        '_total_fees'           => wc_price( $order->get_total_fees(), array( 'currency' => $order->get_currency() ) ),
        'billing_kg'            => get_post_meta( $order_id, '_billing_kg', true );
    );

    return $shipment_data;

}
add_filter( 'wpcwp2p_after_order_completed', 'api_additonal_data', 99, 3 );