union all and order by together

Hi

Im trying to use union all and order by in below sql query .Do help out

select vendor_id

     || '|'|| set_of_books_id

     ||'|'|| TO_CHAR (last_update_date, 'DY MON DD HH24:MI:SS YYYY')

      from ap_invoices_all

     where vendor_id like '%1234%'

union all

select vendor_id

     || '|'|| set_of_books_id

     ||'|'|| TO_CHAR (last_update_date, 'DY MON DD HH24:MI:SS YYYY')

      from ap_invoices_all

     where vendor_id like '%134%'

order by last_update_date;

Im getting ORA-00904: "LAST_UPDATE_DATE": invalid identifier