You can get the Sale Order Number from Table BDCMSGCOLL after you complete BDC all message will contain in the structure Table LT_MSG, loop LT_MSG and let see what SO you will get in the table

DATA :   LT_MSG  TYPE TABLE OF BDCMSGCOLL.

PERFORM BDC_TRANSACTION TABLES LT_MSG
      USING                'VA01'
                                   CTU
                                   MODE
                                   UPDATE.

FORM BDC_TRANSACTION TABLES P_MESSTAB
                     USING  P_TCODE
                            P_CTU
                            P_MODE
                            P_UPDATE.
DATA: L_SUBRC LIKE SY-SUBRC.

  IF P_CTU <> 'X'.
    CALL FUNCTION 'BDC_INSERT'
         EXPORTING  TCODE     = P_TCODE
         TABLES     DYNPROTAB = BDCDATA
         EXCEPTIONS OTHERS    = 1.
  ELSE.
    CALL TRANSACTION P_TCODE USING BDCDATA
                     MODE   P_MODE
                     UPDATE P_UPDATE
                     MESSAGES INTO P_MESSTAB.
  ENDIF.
  L_SUBRC = SY-SUBRC.
  REFRESH BDCDATA.
  SY-SUBRC = L_SUBRC.
ENDFORM.

Tips by : Pim

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