A/R Credit Memo 
For legal reasons, you cannot delete a delivery or invoice that you enter in SAP Business One or change accounting-relevant data in these documents. However, the customer might send the goods back for various reasons, or you may have made a mistake when you entered the documents.
If a sales transaction for which you record an accounting and an inventory posting has been completely or partially reversed, you must enter a corresponding sales document to clear it. This document reverses the changes in terms of inventory quantities and monetary values.
The credit memo is the clearing document for the invoice and for the returns. If the goods were delivered to the customer and an invoice has already been created, you can partially or completely reverse the transaction by creating a credit memo. With the credit memo you correct both the quantities and the monetary values. The system increases the inventory of the credited items by the amount specified in the credit memo. The credit memo credits the value in the customer account in the accounting system and amends the revenue account by the same amount. The system corrects the tax amounts automatically.
SAP Business One enables you to create an A/R credit memo with a zero amount. You can do this when you clear A/R invoices for items delivered without a charge, for example, items that are part of a promotion or covered by a service contract.
When you create an A/R credit memo based on a sales order, you can choose to reopen the item quantity of the order. To be able to do so, the checkbox Enable Reopening of Orders When Creating Returns Based on Orders must be selected in the document settings. For more information, see Document Settings: Per Document Tab.
Reopening the item quantity has the following consequences:
The status of the sales order changes to Open.
The open quantity is increased by the item quantity in the credit memo. If the sum of the remaining open quantity plus the returned quantity is higher than the quantity in the original order, the open quantity is increased up to the quantity in the original order.
The delivered quantity is decreased by the quantity in the credit memo.
For service type transactions, the open amount is increased accordingly by a value equal to the value from a credit memo line. If the sum of the remaining open amount plus the credited amount is greater than the total amount for the original order line, the total amount is used as the open amount.
If there are any freight charges related to the credited item, these charges are reopened in the same way as the item quantities.
If the item is managed by batches, the returned batch-allocated quantity is increased by the quantity from the return line.
To access the window, choose 
Sales – A/R 
A/R Credit Memo 
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Country-Specific Information for Italy
When you create an invoice with a zero amount, note that you must charge VAT on free goods and that the customer has to pay the VAT.
Country-Specific Information for Russia
Due to legal requirements, you must use the credit memo to completely reverse invoices. When you do so, you must modify (cancel) relevant tax invoices accordingly. For more information, see A/P and A/R Tax Invoice - General Information.