I would like to create a partial shipment to manage the reorder
Here is what I am looking for

Customers place the below item
Item1 Quantity 5
Item2 Quantity 10
Item4 Quantity 8

I wanted to ship the available product and the available quantity for the first delivery and then the grater for the second time

Here is the product and the quantity that I have to ship first

Item1 Quantity 1
Item2 Quantity 5
Item4 Quantity 3

Here is my model class

  _orderRepository =   $orderRepository;
        $this->_convertOrder = $convertOrder;
        $this->_trackFactory = $trackFactory;
        $this->_shipmentNotifier = $shipmentNotifier;
        $this->_shipmentFactory = $shipmentFactory;
        $this->_transactionFactory = $transactionFactory;
        $this->_logger = $logger;
        $this->_esnFactory  =   $esnFactory;

    }

    /**
     * Get Shipping update.
     * @api
     * @param ShipmentDataInterface $shipment
     * @return ShipmentDataInterface|void
     * @throws MagentoFrameworkExceptionLocalizedException
     */
    public function saveNewShipment($shipment)
    {
        try{
            $order  =   $this->_orderRepository->get($shipment->getOrderId());
            if($order->canShip()){
                $data   = array(
                    'carrier_code'=>$shipment->getCarrierCode(),
                    'title'=>$shipment->getCarrierTitle(),
                    'number'=>$shipment->getTrackingNumber()
                );
                $orderShipment  =   $this->prepareShipment($order, $data);
                if ($orderShipment){
                    $order->setIsInProcess(true);
                    $order->addStatusHistoryComment('ITEM SHIPPED', false);
                    $transactionSave =  $this->_transactionFactory->create()->addObject($orderShipment)->addObject($orderShipment->getOrder());
                    $transactionSave->save();
                }
               // return $orderShipment;
            }
        }  catch (Exception $e) {
            throw new MagentoFrameworkExceptionLocalizedException(
                __($e->getMessage())
            );
        }


    }

    /**
     * @param $order MagentoSalesModelOrder
     * @param $track array
     * @return $this
     */
    protected function prepareShipment($order, $track)
    {
        $shipment = $this->_shipmentFactory->create(
            $order,
            $this->prepareShipmentItems($order),
            $track
        );
        return $shipment->getTotalQty() ? $shipment->register() : false;
    }
    /**
     * @param $order MagentoSalesModelOrder
     * @return array
     */
    protected function prepareShipmentItems($order)
    {
        $items = ();

        foreach($order->getAllItems() as $item) {
            $items($item->getItemId()) = $item->getQtyOrdered();
        }
        return $items;
    }


}

and here are my postdata with shipping

{
    "shipment": {
        "order_id": 123,
                "carrier_code": "DHLNew",
                "carrier_title": "DHL EXPRESS",
                "tracking_number": "TESTDHL12345",
        "items": (
            {
                "sku": "item1",
                "somedata": "somedata",
                "ShippingBoxNumber": "1",
                "Qty": "1"

            },
            {
                "sku": "item2",
                "somedata": "somedata",
                "ShippingBoxNumber": "1",
                "Qty": "5"
            },
            {
                "sku": "item1",
                "somedata": "somedata",
                "ShippingBoxNumber": "1",
                "Qty": "3" 
            }

        )
    }
}

Every help is appropriated