You can find a sample guide on how to implement this exit in this best practice document: SD/MM - General Settings (263), look for EXIT_SAPLV60B_004 or SDVFX004.
For reference:
- SDVFX002 for A/R line
- SDVFX004 for G/L line
- SDVFX008 for all lines and header of accounting document
Regards,
Raymond