How can I get PR number in ME52N?

I person an enhancement successful ME52N to adhd a header tab. However, I usage beneath coding to get PR fig but failed.

      DATA:  ls_mereqheader TYPE REF TO cl_po_header_handle_mm.
      DATA: lt_header TYPE mepoheader.

      CREATE OBJECT ls_mereqheader.

      CALL METHOD ls_mereqheader->get_data
        IMPORTING
          ex_data = lt_header.

OR

      DATA: dynpfields TYPE TABLE OF dynpread.
      CALL FUNCTION 'DYNP_VALUES_READ'
        EXPORTING
          dyname               = 'SAPLMEGUI' "sy-repid
          dynumb               = '3327'   "sy-dynnr
*         TRANSLATE_TO_UPPER   = ' '
*         REQUEST              = ' '
*         PERFORM_CONVERSION_EXITS             = ' '
*         PERFORM_INPUT_CONVERSION             = ' '
*         DETERMINE_LOOP_INDEX = ' '
*         START_SEARCH_IN_CURRENT_SCREEN       = ' '
*         START_SEARCH_IN_MAIN_SCREEN          = ' '
*         START_SEARCH_IN_STACKED_SCREEN       = ' '
*         START_SEARCH_ON_SCR_STACKPOS         = ' '
*         SEARCH_OWN_SUBSCREENS_FIRST          = ' '
*         SEARCHPATH_OF_SUBSCREEN_AREAS        = ' '
        TABLES
          dynpfields           = dynpfields
        EXCEPTIONS
          invalid_abapworkarea = 1
          invalid_dynprofield  = 2
          invalid_dynproname   = 3
          invalid_dynpronummer = 4
          invalid_request      = 5
          no_fielddescription  = 6
          invalid_parameter    = 7
          undefind_error       = 8
          double_conversion    = 9
          stepl_not_found      = 10
          OTHERS               = 11.
      IF sy-subrc <> 0.
* Implement suitable error handling here
      ENDIF.

What is incorrect for the supra coding? oregon immoderate different mode to get the PR number? Thanks successful advance.