QuickBooks-V3-DotNET-SDK: Batch operation throws when creating Customer with a ParentRef

Even though I am specifying a ParentRef, the batch.Execute() operation keeps throwing “Validation Exception was thrown.Details:ParentRef is either required or not if Job is true or false…”

var customer = new Customer();
customer.DisplayName = "Aything";
customer.IsProject = true;
customer.BillWithParent = true;
customer.Job = true;
customer.ParentRef = new ReferenceType { Value = "123" };

batch.Add(customer, "bID1", OperationEnum.create);

What is wrong here? The Value specified in the ReferenceType is of an existing Customer in QuickBooks.