CREATE OR REPLACE FUNCTION paybase_schema.test123 (v_input integer) RETURNS smallint AS
$body$
DECLARE
BEGIN
  return v_input;
END;
$body$
LANGUAGE 'plpgsql'
VOLATILE
CALLED ON NULL INPUT
SECURITY INVOKER
COST 100;

select "paybase_schema"."test123"@pgsql(1) from dual

create or replace function call_func(v_func varchar2) return number is
 v_cursor binary_integer;
 v_nr binary_integer;
 v_ret number;
begin
 v_cursor := dbms_hs_passthrough.open_cursor@pgsql;
 dbms_hs_passthrough.parse@pgsql(v_cursor, 'select ' || v_func) ;
 v_nr := dbms_hs_passthrough.fetch_row@pgsql(v_cursor);
 dbms_hs_passthrough.get_value@pgsql(v_cursor, 1, v_ret);
 dbms_hs_passthrough.close_cursor@pgsql(v_cursor);
 return v_ret; 
end; 

select call_func('paybase_schema.test123(777)') as rez from dual

CREATE OR REPLACE FUNCTION paybase_schema.test123 (v_input numeric) RETURNS numeric AS
$body$
DECLARE
BEGIN
  return v_input;
END;
$body$
LANGUAGE 'plpgsql'
VOLATILE
CALLED ON NULL INPUT
SECURITY INVOKER
COST 100;

select call_func('paybase_schema.test123(1.25)') as rez from dual