When I run the following code, I see the correct results in l_context, but nothing downloads. What am I missing? How can I troubleshoot this since there are no errors?

  l_context := apex_exec.open_query_context(
        p_location    => apex_exec.c_location_local_db,
        p_sql_query   => 'select output from TFA_USER',
        p_where_clause => :P0_SUB );

    l_export := apex_data_export.export (
        p_context   => l_context,
        p_format    => apex_data_export.c_format_json,
        p_file_name => 'test' );

    apex_exec.close( l_context );

    apex_data_export.download( p_export => l_export );

EXCEPTION
    when others THEN
        apex_exec.close( l_context );
        raise;
DBMS_OUTPUT.put_line(l_context);
  APEX_JSON.free_output;
  end;