Message type: E = Error
Message class:  FKK_ID_HU - FICA#Hungary 
Message number: 004
Message text: Due date for net payment cannot be changed
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 FKK_ID_HU004 indicates that the due date for net payment cannot be changed. This error typically arises in the context of contract accounts receivable and payable (FI-CA) when there is an attempt to modify the due date of a payment that is already set or has been processed.
Cause: Payment Terms: The payment terms associated with the invoice or contract may not allow for changes to the due date once it has been established. Document Status: The document may be in a status that does not permit changes, such as being already posted or cleared. Configuration Settings: There may be specific configuration settings in the system that restrict changes to due dates for certain types of documents or accounts. Legal or Compliance Restrictions: In some cases, legal or compliance requirements may prevent changes to payment terms or due dates.
Solution: Check Document Status: Verify the status of the document. If it has already been
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
FKK_ID_HU003 Entry already exists in recording table for &1
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
FKK_ID_HU002 Company code is invalid
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
FKK_ID_IN000 *************************************************************************
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
FKK_ID_IN001 Full or None option choosen for Company Code, so no partial payment made.
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
Click on this link to search all SAP messages.