Alv top of page header text is not displaying

Dear All.

Please find my program details . Top of Page header text is not displaying in Alv output. Please  I need your suggest ...

*&---------------------------------------------------------------------*
*&      Form  DISPLAY
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
*  -->  p1        text
*  <--  p2        text
*----------------------------------------------------------------------*
form DISPLAY .

  CALLFUNCTION'REUSE_ALV_GRID_DISPLAY'
  EXPORTING

    I_CALLBACK_PROGRAM                = 'SY_REPID'
*   I_CALLBACK_USER_COMMAND          = ' '
    I_CALLBACK_TOP_OF_PAGE            = 'TOP-OF-PAGE'
*   I_GRID_TITLE                     = 'PACKING SLIP(BOX WISE) DETAILS'
*   IS_LAYOUT                        =
*   IT_EVENTS                         = I_EVENTS
    IT_FIELDCAT                       = I_FCAT

   TABLES
     t_outtab                         = ITAB_FINAL
           .

endform.                    " DISPLAY

**&--------------------------------------------------------------------*
**& Form TOP_OF_PAGE
**&--------------------------------------------------------------------*
** text
**---------------------------------------------------------------------*
FORM TOP-OF-PAGE.

****Declaration of Header
DATA:IT_HEADER TYPE SLIS_T_LISTHEADER,
      WA_HEADER LIKELINEOF IT_HEADER,
      T_LINE LIKE WA_HEADER-INFO,
      LD_LINES TYPEI,
      LD_LINESC(10) TYPEC.

**Title
  WA_HEADER-TYP = 'H'.
  WA_HEADER-INFO = 'PACKING SLIP(BOX WISE) DETAILS'.
  APPEND WA_HEADER TO IT_HEADER.
  CLEAR WA_HEADER.


* *Invoice Number
   WA_HEADER-TYP  = 'S'.
   WA_HEADER-INFO = 'Invoice Number : '.
   WA_HEADER-KEY = P_EXNUM.
   APPEND WA_HEADER TO IT_HEADER.
   CLEAR WA_HEADER.


   callfunction'REUSE_ALV_COMMENTARY_WRITE'
     exporting
       it_list_commentary = IT_HEADER
       i_logo             = 'NCLLOGO'.

endform.                    " TOP-OF-PAGE