Ajax投票系统

I assume that I don't know a lot of jquery and ajax, I'm venturing trying to be able to create a "like" button. I use codeigniter 4, for the moment I have created a simple function in the controller, passing the post ID and entering the query (it's all simple because I need to understand and make it work for the moment).

Unfortunately, however, I have various problems, I believe that it does not pass the data in the ajax code via the data-id placed in

What am I doing wrong? or better, what should I add?

$('.like').on("click",function(){
    var post_id = $('a').attr('data-id');
    $.ajax({
        type: "POST",
        url: '<?= site_url('auth/sendVote'); ?>',
        data: "post_id="+post_id,
        cache: false,
        success: function(response){
            $().html(response+"");
        }
    });
});



<a href="" class="like card-btn" data-id="<?= $item['id']; ?>">
<div class="total ml-auto">
     <?= $model->countVotes($item['id']); ?>
</div>
</a>