$nid as tag

I wanna link node and comment for same function as sum votes by node. Why it doesn't work?

create vote

 $votes[] = array(
    'content_type' => 'comment',
    'content_id' => $cid,
    'value_type' => 'points',
    'value' => $value,
    'tag' => $nid,
    );
    votingapi_set_votes($votes);

sum

$results = votingapi_select_results($criteria = array (
'tag' => $nid,
'function' => 'sum',)
);

Please, help)