ORA-00998: must name this expression with a column alias

I am createing this view, and getting this error:  ORA-00998: must name this expression with a column alias

and where the SUM (k.reconciliation_amount),  IS GETTING HIGHLIGHTED. any suggestions

CREATE OR REPLACE VIEW ENVIRON.REC_AMT_TICKET_SET_SH_VIEW
AS
SELECT   a.initial_fileset_id, a.ticket_set_key, a.business_process_type,
         a.country_code, a.company_code, a.project_code, b.data_object_code,
         c.run_id, b.data_object_name, b.data_object_description,
         d.data_object_recon_stage_sort, e.data_object_recon_unit_sort,
         f.data_object_recon_type_sort, g.recon_type_name, g.recon_type_group,
         g.recon_type_sub_group, h.recon_stage_name, h.recon_stage_system,
         h.recon_stage_function, i.recon_item_name, i.recon_by_amount,
         i.recon_by_count, j.recon_unit_name, a.reconciliation_status,
         SUM (k.reconciliation_amount), k.currency_type
    FROM setup.data_object b,
         setup.data_object_recon_item,
         setup.data_object_recon_stage d,
         setup.data_object_recon_type f,
         setup.data_object_recon_unit e,
         setup.recon_item i,
         setup.recon_stage h,
         setup.recon_type g,
         setup.recon_unit j,
         environ.amount_reconciliation k,
         environ.recon_figure,
         environ.ticket_set a,
         environ.ticket_set_run_rerun c
   WHERE (    (b.data_object_code = data_object_recon_item.data_object_code)
          AND (b.data_object_code = d.data_object_code)
          AND (b.data_object_code = f.data_object_code)
          AND (b.data_object_code = e.data_object_code)
          AND (i.recon_item_id = data_object_recon_item.recon_item_id)
          AND (h.recon_stage_id = d.recon_stage_id)
          AND (g.recon_type_id = f.recon_type_id)
          AND (j.recon_unit_id = e.recon_unit_id)
          AND (i.recon_item_id = recon_figure.recon_item_id)
          AND (h.recon_stage_id = recon_figure.recon_stage_id)
          AND (g.recon_type_id = recon_figure.recon_type_id)
          AND (j.recon_unit_id = recon_figure.recon_unit_id)
          AND (recon_figure.recon_figure_id = k.recon_figure_id)
          AND (b.data_object_code = c.data_object_code)
          AND (a.initial_fileset_id = c.initial_fileset_id)
          AND (a.ticket_set_key = c.ticket_set_key)
          AND (c.ticket_set_run_rerun_id = k.ticket_set_run_rerun_id)
         )
GROUP BY a.initial_fileset_id,
         a.ticket_set_key,
         a.business_process_type,
         a.country_code,
         a.company_code,
         a.project_code,
         b.data_object_code,
         c.run_id,
         b.data_object_name,
         b.data_object_description,
         d.data_object_recon_stage_sort,
         e.data_object_recon_unit_sort,
         f.data_object_recon_type_sort,
         g.recon_type_name,
         g.recon_type_group,
         g.recon_type_sub_group,
         h.recon_stage_name,
         h.recon_stage_system,
         h.recon_stage_function,
         i.recon_item_name,
         i.recon_by_amount,
         i.recon_by_count,
         j.recon_unit_name,
         a.reconciliation_status,
         k.currency_type