• This error is shown while posting MIRO document.
• You are using Funds Management in an S/4HANA
• It will be displayed when
  • The derivation strategy overwrites the WRX line with another account assignment than the one existing in the PO.
  • The PO that makes reference in the MIRO document was created before PSM-FM was actived.
    • If you dont want to make the PO now updates PSM-FM you can jump to section: "Converting the error into warning"
  • The PO has a commitment item not relevant (Financial transaction <> 30) and the MIRO posting has the same commitment item inherited from the PO in the GR/IR clearing account line (WRX line).
    • Make sure following note is implemented in your system: 3131982 - S/4HANA: Consistency check message FICUSTOM401 at MIRO
• This is done to ensure the whole chain of documents (PO-GR-IR) have the same account assignment and it is consistent.
• This may happen with any of the account assignemnts:
  • Commitment item
  • Funds center
  • Fund
  • Budget period
  • Functional Area
  • Funded program
  • Grant

Locating error in FMDERIVE trace

To detect the error it is needed to compare the account assignment that has been posted in the PO (transaction ME23N or FMIOI table) and the one that is being derived in the FMDERIVE.

In this case, in ME23N:

And the FMDERIVE trace:

As the FMDERIVE trace is displayes several times, we need to focus in the one that:

Transaction = WRX 
Ref transaction = RMRP
Process Detail = IR_CLR

In this case, we can see the funds center is different in the FMDERIVE and the ME23N, so this field is causing the error. 

In FMDERIVE it is 10201 and in ME23N it is 10101.

Detecting the erroneous step

At the time FMDERIVE is displayed the different account assignment (in this case the funds center)  we need to check the step that is causing this mismatch. So, we  will need to open the log for the FMDERIVE and detect the one that is overwritting the funds center. Normally the steps will have an "overwrite target value" condition.

Fixing the error

There are several ways to fix the error depending on your business processes and the way MIRO must be updated.

First of all it is necessary to decide whether we want the MIRO is updated wiht the same account assignment that exists in PO or not.

• If the account assignment must be the same in PO and MIRO:

Then the best way is to use the Function Module FMDT_READ_PO_ASSIGNMENT. This way the account assignment is directly read from the PO.

Example in FMDERIVE:

Source fields:
In this case would be PO document number, line item and account assignmnet number.

Target fields:
It is necessary to set as "overwrite with new value" to ensure the value from the PO is the one taken.

Condition: There it is necessary to limit this derivation rule only when the process is IR_CLR (as we are processing MIRO)

• If the account assigment must be / can be different in PO and MIRO:

Converting the error into warning

Then it is possible to turn the FICUSTOM401 into warning in OBA5 transaction. But ALWAYS taking into account if its turned into warning or supressed, it will be for all postings from that moment on. 

More info

For more info, refer to note 2491908 FICUSTOM401: FMDERIVE Consistency Check 01 error during WRX RMRP