You are using a Data store Operation of the type Write.

To avoid duplicate entries when using a Data Store Operation of the type Write, you must select the Overwrite Existing Message parameter. The Overwrite Existing Message parameter allows you to overwrite an existing data store entry with the same key if it already exists. If you do not select this parameter, the Write operation will fail if there is a duplicate key in the data store. References:  Modernize Integration with SAP Integration Suite | openSAP