I have added a new custom field in table BUT000. Now i want to update that field with 'X' and i have used EXTENSIONIN parameter in the BAPI 'BAPI_ISUPARTNER_CHANGE'. i have populated the field name(Custom field name) and value 'X' to that structure and passed to BAPI. But that field value was not getting updated. So can any one help me how to resolve this issue.