Use FM POPUP_WITH_TABLE_DISPLAY_OK :

Example to display a long text :
DATA lt_message TYPE STANDARD TABLE OF text75.
lt_message = VALUE #( ( 'I can use this popup to display long messages :' )
( 'Lorem ipsum dolor sit amet, consectetur adipiscing ' )
( 'elit.' )
( 'Donec vitae risus eros. Nunc dolor ante, venenatis ' )
( 'eget neque vitae, egestas ullamcorper ipsum. ' )
( 'In sed arcu ac dolor facilisis vulputate. Proin odio est,' )
( 'molestie quis hendrerit scelerisque, vulputate id tortor.') ).
CALL FUNCTION 'POPUP_WITH_TABLE_DISPLAY_OK'
EXPORTING
endpos_col = 80
endpos_row = 20
startpos_col = 20
startpos_row = 10
titletext = 'Title Not working'
* IMPORTING
* CHOISE =
TABLES
valuetab = lt_message
EXCEPTIONS
break_off = 1
OTHERS = 2.
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