["code"]=>
          string(23) "INSUFFICIENT_PERMISSION"
          ["message"]=>
          string(292) "You do not have permissions to set a value for element inventoryassignment.receiptinventorynumber 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."

$service = new NetSuiteService();

$salesOrderInternalID = "330536";

$reference = new InitializeRef();
$reference->type = InitializeRefType::salesOrder;
$reference->internalId = $salesOrderInternalID;

$record = new InitializeRecord();
$record->type = InitializeType::itemFulfillment;
$record->reference = $reference;

$request = new InitializeRequest();
$request->initializeRecord = $record;

$initResponse = $service->initialize($request);
//vd($initResponse);

if (!$initResponse->readResponse->status->isSuccess) {
    echo "INIT ERROR";
    exit();
}
$itemFulfillment = $initResponse->readResponse->record;

foreach($itemFulfillment->itemList->item as $item) {
//$lineItemId = $item->item->internalId;

    $inventoryAssignment = new InventoryAssignment();
    $inventoryAssignment->quantity = 9;
    $inventoryAssignment->receiptInventoryNumber = "011546";

    $inventoryAssignmentList = new InventoryAssignmentList();
    $inventoryAssignmentList->inventoryAssignment = $inventoryAssignment;

    $inventoryDetail = new InventoryDetail();
    $inventoryDetail->inventoryAssignmentList = $inventoryAssignmentList;

    $item->inventoryDetail = $inventoryDetail;
}

$addRequest = new AddRequest();
$addRequest->record = $itemFulfillment;
$addResponse = $service->add($addRequest);
//vd($addResponse);
if (!$addResponse->writeResponse->status->isSuccess) {
    echo "ADD ERROR";
    exit();
}
$fulfillmentInternalId = $addResponse->writeResponse->baseRef->internalId;
echo "Item Fulfillment created with internal ID: " . $fulfillmentInternalId;

["issueInventoryNumber"]=>
object(RecordRef)#33 (4) {
["name"]=>
string(7) "2942206"
["internalId"]=>
string(4) "8659"
["externalId"]=>
NULL
["type"]=>
NULL
}

object(InventoryAssignment)#32 (10) {
["internalId"]=>
string(6) "384752"
["issueInventoryNumber"]=>
object(RecordRef)#33 (4) {
["name"]=>
string(7) "2942206"
["internalId"]=>
string(4) "8659"
["externalId"]=>
NULL
["type"]=>
NULL
}
["receiptInventoryNumber"]=>
NULL
["binNumber"]=>
NULL
["toBinNumber"]=>
NULL
["quantity"]=>
float(1)
["expirationDate"]=>
string(29) "2025-11-06T16:00:00.000-08:00"
["quantityAvailable"]=>
float(128)
["inventoryStatus"]=>
NULL
["toInventoryStatus"]=>
NULL
}