Message type: E = Error
Message class:  IDFI_VAT_PR - VAT Pro-Rata 
Message number: 028
Message text: Posting parameter credit VAT account is mandatory
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 IDFI_VAT_PR028, which states "Posting parameter credit VAT account is mandatory," typically occurs during the posting of transactions that involve VAT (Value Added Tax). This error indicates that the system requires a credit VAT account to be specified in the posting parameters, but it has not been provided.
Cause: Missing Configuration: The credit VAT account may not be configured in the relevant financial document or posting parameters. Incorrect Account Assignment: The account assignment for the transaction may not include a valid credit VAT account. Transaction Type: The type of transaction being posted may require a credit VAT account, but it has not been set up correctly in the system. Master Data Issues: The master data for the vendor or customer may not have the necessary VAT account information.
Solution: Check Configuration: Go to the configuration settings for VAT accounts in the SAP system. Ensure that the credit VAT account is defined for the relevant transaction
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
IDFI_VAT_PR027 Posting parameter debit VAT account is mandatory
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
IDFI_VAT_PR026 Posting parameter credit tax code is mandatory
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
IDFI_VAT_PR029 Posting parameter debit G/L account for services is mandatory
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
IDFI_VAT_PR030 Posting parameter credit G/L account for services is mandatory
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.