SAP Message V4343 - External document number &1 does not match reference document number &2

Diagnosis The external document number sent in the IDoc was not correctly copiedinto the newly created invoice. System Response The IDoc ends with status 51. Procedure Check: - Whether the external document number was sent correctly in the IDoc.The document number is transferred in segment E1EDK01, field DOCNO. - Whether a correct copy routine is set up. In the standard deliverycopying requirement 024 or 025 is provided at item level for copyingfrom delivery to billing. This transfers the document number sent froman external source.