How we can create partial shipment programmatically using rest api

Boe,

Here is the way to create partial shipment.

you have to pass orderItemId and Qty to ship

Class ShipmentAPI{

    protected $_shipOrderInterface;

    public function __construct(
     \Magento\Sales\Api\ShipOrderInterface $shipOrderInterface
    ){
        $this->_shipOrderInterface = $shipOrderInterface;
    }

    public function createShipment($orderId){

        $shipmentItems = [ "29" => 2 ];
        $shipmentId = 0;    
        if(count($shipmentItems) > 0){

            foreach($shipmentItems as $orderItemId => $qty){
                $itemCreation = $this->_shipmentItemCreationInterface;
                $itemCreation->setOrderItemId($orderItemId)->setQty($qty); 

                $shipItem[] = clone $itemCreation;              

            }
            $shipmentItem = $this->_shipmentInteface->setItems($shipItem);

            $_items = [];
            if(count($shipmentItem->getItems()) > 0 ){
                $_items = $shipmentItem->getItems();    
            }

            $shipmentId = $this->_shipOrderInterface->execute( 
                $orderId, 
                $_items, 
                $notify = false,
                $appendComment = false,
                $comment = null,  
                $shipmentTracks
            );  
        }

        return $shipmentId;
    }
}

this function will give you shipmentId after passing the items properly. Hope this will help you.

A bit of a simpler solution that worked perfectly for me:

$shipmentItems = [
    $this->shipmentItemCreation->setOrderItemId(1234)->setQty(1)
];

$this->shipOrder->execute($orderId, $shipmentItems, $notify, $appendComment, $comment, $tracks, $packages, $arguments);

Where $this->shipItemCreation is an instance of \Magento\Sales\Api\ShipOrderInterface and $this->shipOrder is an instance of \Magento\Sales\Api\ShipOrderInterface.

The above example creates a shipment with 1 unit of the order item ID 1234.