// Declare variables
ICreditMemoAdd creditMemoAddRq = requestMsgSet.AppendCreditMemoAddRq();

// Set the following properites
// Customer by QuickBooks ID
creditMemoAddRq.CustomerRef.ListID.SetValue(creditMemo.Customer.QuickBooksID);

// Required
// Accounts Receivable by QuickBooks ID
creditMemoAddRq.ARAccountRef.ListID.SetValue(creditMemo.Account.QuickBooksID);

// Invoice Template by QuickBooks ID
creditMemoAddRq.TemplateRef.ListID.SetValue(creditMemo.Template.QuickBooksID);

// Date
creditMemoAddRq.TxnDate.SetValue(creditMemo.Date);

// Ship Date
creditMemoAddRq.ShipDate.SetValue(creditMemo.ShipDate);

// Due Date
if (creditMemo.DueDate.Year > 2000)
    creditMemoAddRq.DueDate.SetValue(creditMemo.DueDate);

// Memo (if set)
creditMemoAddRq.Memo.SetValue(creditMemo.Memo ?? string.Empty);

//Set field value for IsToBePrinted
creditMemoAddRq.IsToBePrinted.SetValue(false);

//Set field value for IsToBeEmailed
creditMemoAddRq.IsToBeEmailed.SetValue(false);

// Add each line item
foreach (LineItemDto lineItem in creditMemo.LineItems)

{

    // Declare variables
    IORCreditMemoLineAdd lineItemAdd = creditMemoAddRq.ORCreditMemoLineAddList.Append();

    // Add a line item
    if (lineItem.Type == LineItemDto.Types.LineItem)
    {
        // Line Item by QuickBooks ID
        lineItemAdd.CreditMemoLineAdd.ItemRef.ListID.SetValue(lineItem.QuickBooksID);

        // Description
        lineItemAdd.CreditMemoLineAdd.Desc.SetValue(lineItem.Description ?? string.Empty);

        // Quantity
        lineItemAdd.CreditMemoLineAdd.Quantity.SetValue(lineItem.Quantity);

        // Amount
        lineItemAdd.CreditMemoLineAdd.Amount.SetValue(lineItem.Amount);

    }
}