How To Fix FKKBIX639 - The interface of function module &1 is not correct

FKKBIX639 - Overview

• Message type: E = Error

• Message class: FKKBIX - Conv.Inv.: Billing (Invoice Preprocessing)

• Message number: 639

• Message text: The interface of function module &1 is not correct

What causes this issue?

Make sure that you use the templates described in the following links:
<DS:DE.DISC_BASE_EXIT_KK>Determination of the base quantity using a
function module</>
<DS:DE.DISC_CALC_RULE_EXIT_KK>Calculation rule in function module</>
<DS:DE.DISC_COND_RULE_EXIT_KK>Condition rule in function module</>

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.

FKKBIX639 - Details

• The SAP error message FKKBIX639 indicates that there is an issue with the interface of a function module. This error typically arises when the parameters defined in the function module do not match the expected parameters in the calling program or when there are inconsistencies in the data types or structures.
  
  Cause:
  
  Mismatch in Parameters: The function module being called has parameters that do not match the expected parameters in the calling program. This could be due to changes in the function module interface that have not been reflected in the calling program.
  Data Type Issues: The data types of the parameters being passed may not be compatible with those defined in the function module.
  Missing Parameters: Required parameters may be missing in the call to the function module.
  Changes in Function Module: If the function module was recently modified (e.g., added or removed parameters), the calling program may not have been updated accordingly.
  
  
  Solution:
  
  Check Function