Message type: E = Error
Message class:  FAGL_POSTING - Messages for FAGL_POSTING EhP3 Relating to New Functions 
Message number: 013
Message text: Clearing specific to ledger group only with transaction FB1SL or FB05L
The <LS>Clearing Specific to Ledger Groups</> indicator is set for
account &V1&.
Clearing on accounts with this indicator can only be performed with the
transactions <AB>FB05L</> (<LS>Post with Clearing for Ledger Group</>)
<AB>FB1SL</> (<LS>Clear G/L Account for Ledger Group</>).
Processing is not possible.
Use transaction <AB>FB05L</> or <AB>FB1SL</>.
The system issues an error message and will not allow you to continue with this transaction until the error is resolved.
Error message extract from SAP system. Copyright SAP SE.
The SAP error message FAGL_POSTING013 indicates that a clearing operation is restricted to a specific ledger group when using the transactions FB1SL (Post Document) or FB05L (Clear Document). This error typically arises in the context of the New General Ledger (New GL) functionality in SAP, where different ledger groups can be defined for various reporting and accounting purposes.
Cause: The error occurs when: You are trying to clear items that belong to different ledger groups. The configuration of the ledger groups does not allow for clearing across different groups. The document you are trying to post or clear is not compatible with the ledger group settings.
Solution: To resolve the FAGL_POSTING013 error, you can take the following steps: Check Ledger Group Settings: Ensure that the items you are trying to clear belong to the same ledger group. You can check the ledger group assigned to each document in the document display (transaction FB03). Use the Correct Transaction: If you need to
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