Replicate BUPA_REL custom field to ECC

Hello,

I have enhanced BUPA_REL BDoc with a custom field and I have problem with its replication to ECC. I checked event SMOUTIL2, custom data is available in  BAPIMTCS table. I also created function modules for 2 BTE in ECC - for DE_BALE and for CRM0_300. I debugged all user exits in ECC - custom relationship field is available when CRM0_300 is called. However, when execution comes to event DE_BALE it is already gone. I don't have the custom field in ERP, because I want to update a standard field - KNVP-KNREF and I thought I can do it directly in DE_BALE FM by changing idoc_data.

But BAPIMTCS table does not contain the needed data.

Please help.

Kind regards,

Desislava