A/P Credit Memo 
When you create a delivery for a purchase order or an A/P invoice in SAP Business One, legal stipulations prevent you from deleting or making any changes to these documents. You may, however, want to return the goods to the vendor for a variety of reasons, or you may find that you have made a mistake while creating the documents.
The A/P credit memo is the clearing document for the A/P invoice. Therefore, if the vendor has delivered goods, and you have already created an A/P invoice, you can reverse the transaction either partially or completely by creating an A/P credit memo.
You create the A/P credit memo based on the A/P invoice to establish a link between the two transactions in SAP Business One. However, it is also possible to create an A/P credit memo without having a base document.
SAP Business One lets you create an A/P credit memo with a zero amount. You can do this when you clear A/P invoices for no-charge items, such as items that are part of a promotion or covered by a service contract.
You correct both the quantities and the values with the credit memo. SAP Business One reduces the inventory of the credited items by the quantity specified in the credit memo, posts the value of the credit memo to the vendor account in the accounting system, and reduces the expense account by the same amount.
Note
You cannot post to an expense account when the item is an inventory item or the company is a perpetual inventory company.
Note
If you have returned goods to a vendor, and received only a goods return document, enter it into SAP Business One. When the A/P credit memo is received from the vendor, create it in SAP Business One using the goods return as a base document. That way, the A/P credit memo updates the financial values only, while quantities and inventory values are updated by the goods return document.
When you create an A/P credit memo for service, there is no significance to goods returns, since only the financial values are updated.
When you create an A/P credit memo based on a purchase 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 purchase 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 will be increased by the quantity from the return line.
To access the window, choose 
Purchasing – A/P 
A/P Credit Memo 
.
Country-Specific Information: 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: Russia
Due to legal requirements, you must use only credit memos to completely reverse invoices. When you do so, you must modify or cancel the relevant tax invoices accordingly. For more information, see A/P and A/R Tax Invoice - General Information.