Link Purchase Order to Sales Order C#

Guys,

I’m trying to automate linking the purchase order to a sale order and the following is the code I tried to accomplish this task. But I face error. Can you please check and let me know what I’m missing here

Purchase Order Creation: 

var createPurchaseOrder = new PurchaseOrder();

createPurchaseOrder.entity = new RecordRef()
{
internalId = “653”
//type = RecordType.purchaseOrder,
//typeSpecified = true
};

RecordRef soRecordRef = new RecordRef();
soRecordRef.internalId = “XXXXXXXX”;
soRecordRef.type = RecordType.salesOrder;
soRecordRef.typeSpecified = true;

createPurchaseOrder.createdFrom = soRecordRef;

RecordRef depRecordRef = new RecordRef();
depRecordRef.internalId = “3”;
depRecordRef.name = “eBay : eBay FNC”;
depRecordRef.type = RecordType.department;
depRecordRef.typeSpecified = true;

createPurchaseOrder.department = depRecordRef;

PurchaseOrderItem[] Items = new PurchaseOrderItem[1];

Items[0] = new PurchaseOrderItem();
RecordRef item = new RecordRef();
item.type = RecordType.nonInventoryPurchaseItem;
item.typeSpecified = true;
item.internalId = “XXXXX”;
Items[0].item = item;

Items[0].rate = “5”;
Items[0].quantity = 1;
Items[0].quantitySpecified = true;

PurchaseOrderItemList purchaseOrderItemList = new PurchaseOrderItemList();
purchaseOrderItemList.item = Items;
createPurchaseOrder.itemList = purchaseOrderItemList;

WriteResponse response = Service.add(createPurchaseOrder);

Update Purchase Order Number in Sales Order 

var updateSalesOrder = new SalesOrder();
updateSalesOrder.internalId = “XXXXXXXX”;

SalesOrderItem[] soItems = new SalesOrderItem[1];

var soItem = new SalesOrderItem();

RecordRef roItem = new RecordRef();
roItem.type = RecordType.inventoryItem;
roItem.typeSpecified = true;
roItem.internalId = “XXXXX”;
soItem.item = roItem;

RecordRef prLevel = new RecordRef();
prLevel.type = RecordType.priceLevel;
prLevel.internalId = “-1”;
prLevel.typeSpecified = true;

soItem.price = prLevel;
soItem.rate = “15”;
soItem.quantity = 1;
soItem.quantitySpecified = true;

RecordRef poItem = new RecordRef();
poItem.type = RecordType.purchaseOrder;
poItem.typeSpecified = true;
poItem.internalId = purchaseOrder.internalId;
soItem.createdPo = poItem;

soItems[0] = soItem;

SalesOrderItemList salesOrderItemList = new SalesOrderItemList();
salesOrderItemList.item = soItems;
updateSalesOrder.itemList = salesOrderItemList;

response = Service.update(updateSalesOrder);
if (response.status.isSuccess != true) throw new Exception(response.status.statusDetail[0].message);

Error which i get:

You do not have permissions to set a value for element createPOSpecified due to one of the following reasons: 1) The field is read-only; 2) An associated feature is disabled; 3) The field is available either when a record is created or updated, but not in both cases.

Note: createPOSpecified is not displayed in the sales order screen in NetSuite. When I try to update a field in the sales order which exist in the form, then I am able to update it successfully but the field I am trying to update (createPOSpecified ) is not available in this sales form. In this case how can I update this ? Also is this the better way of linking the purchase order with sales order?

Thanks in Advance.