Explain Reversal of Documents in SAP?

If you need to change some of the accounting information relating to an already posted document, you can only achieve this by reversing the original document and posting a new one with the correct information. However, reversal is possible only when:

􀂃 The origin of the document is in FI (not through SD or MM, etc.)

􀂃 The information such as business area, cost center, etc., is still valid (that you have not deleted these business objects)

􀂃 The original document has no cleared items

􀂃 The document relates only to the line items of customer/vendor/GL

While reversing, the system automatically selects the appropriate document type for the reversal, and defaults the relevant posting keys. (Remember that the document type for the reversal document would have already been configured when the document type was defined in the configuration.) Also note that if you do not specify the posting date for the reversal document, the system defaults to the posting date of the original document.