REUSE_ALV_FIELDCATALOG_MERGE column name not displayed

Hi i am using REUSE_ALV_FIELDCATALOG_MERGE for generating field catalog for the internal table output is basically a structure. so for the input values

i have provided both table and structure as below.

I_INTERNAL_TABNAME           = 'FKKBIXBIT0_IT_DISP_TAB'

I_STRUCTURE_NAME             =  'FKKBIXBIT0_IT_DISP' "

to use the field catalog for the OOPS i have moved the field catalog to variable type SLIS_FIELDCAT_ALV. When SET_TABLE_FOR_FIRST_DISPLAY is used the internal table data appears in output but column names were not displayed. Please guide me.

Thanks,

Ganesh.