Message type: E = Error
Message class:  J_3RF_DDX - Message class for digital documents exchange 
Message number: 208
Message text: Incorrect key for Outgoing Invoice
Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of messages in the SAP system have a message text, however this is frequently insufficient to comprehend or resolve the problem.
To make things easier, more detailed information is frequently added to describe the issue, how to fix it, and the necessary steps or configuration modifications.
Unfortunately, there isn't any extra information in this error notice.
First, use our AnswerBot below to get a possible cause and solution (requires a premium subscription).
Also, review the in-depth Common Questions & Answers listed below; you could discover a solution there or be able to connect with others who have faced similar challenges.
You can also try searching the SAP support portal (support.sap.com) but you need a special user ID to access it. It is possible that an SAP support note exists that provides additional details about the mistake or even steps for fixing it.
The SAP error message J_3RF_DDX208 "Incorrect key for Outgoing Invoice" typically occurs in the context of the SAP system when dealing with outgoing invoices, particularly in the area of tax reporting or electronic invoicing. This error can arise due to various reasons, and understanding the cause is crucial for finding an appropriate solution. Causes: Incorrect Document Key: The error may indicate that the document key (which could be a combination of fields like invoice number, company code, fiscal year, etc.) does not match the expected format or does not exist in the system. Data Inconsistencies: There may be inconsistencies in the data related to the outgoing invoice, such as missing or incorrect entries in the relevant tables.
Configuration Issues: Incorrect configuration settings in the SAP system related to invoicing or tax reporting can lead to this error. Authorization Issues: The user may not have the necessary authorizations to access or process the outgoing invoice. Integration Issues:
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
J_3RF_DDX207 Incorrect key for Incoming Invoice
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
J_3RF_DDX206 NUMBER_GET_NEXT error in Journal (object J_3RINV)
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
J_3RF_DDX209 Output type for billing document & is not defined
What causes this issue?  Output type for XML generation is not defined.System Response  The system issues an error message and will not allow you to c...
J_3RF_DDX210 Correspondence type for FI document & & is not defined
What causes this issue?  Correspondence type for XML generation is not defined.System Response  The system issues an error message and will not allow ...
Click on this link to search all SAP messages.