Diagnosis
There are 3 types of reversal:
1) Business case reversal
Req. fields AKTYP = 01
BLTYP = 99
REFGF
2) Partner/contract reversal
Req. fields AKTYP = 01
BLTYP = 99
GPART
VTREF
3) Payment plan reversal
Req. fields AKTYP = 01
BLTYP = 99
GPART
VTREF
POSNR