Hi,
Basically the segment E1IDBW1 will always be filled via user exit.
If you work with the IHC (In-House-Cash) application you have to fill
the E1IDBW1 segment as described in note 626577.
If you don't work in an IHC environment the following conditions must
be fulfilled:
1. The payment program has to fill certain fields (e. g. REGUH-DTAWS,
REGUH-DTWS1 - REGUH-DTWS4).
2. If this is fulfilled the payment data (REGUH, REGUP tables) will
be filled. The instruction keys will be moved to IDOC segment
E1IDKU3.
3. In user exit EXIT_SAPLIEDP_002 you can take over the instruction
keys from segment E1IDKU3 into E1IDBW1.
You may also read note 496663, this note explains about user exit
EXIT_SAPLIEDP_002 to populate this field in the idoc.
Also, you can check the note:
580321 - RFFOEDI1: BTE process 00002441 (Change IDoc)
REgards,
Cristiano