Ajax cannot display the response from php - php

Question

I know that this question is already answered a lot, but even the previous responses from php are working, this response cannot work and i cannot find the reason for this issue.
Although php was send the response succesfully, ajax cannot display without refreshing the page first.
Here is my jquery.ajax code in the file helpers.js:
function likeButton(commentId, userId) {
$.ajax({
url: "requests.php",
type: "POST",
data: {
like: "likeUp",
commentId: commentId,
userId: userId
},
success: function(response) {
$("#comment_body").append(response);
}
});
}
Here is my php code in requests.php:
if(isset($_POST['like'])) {
if($_POST['like'] == "likeUp") {
$commentId = $_POST['commentId'];
$userId = $_POST['userId'];
$sql = "SELECT gaming_comment_like FROM gaming_comments WHERE gaming_comment_id='$commentId'";
$result = mysqli_query($conn, $sql);
if($row = mysqli_fetch_assoc($result)) {
$gaming_comment_like = $row['gaming_comment_like'];
}
$gaming_comment_like = $gaming_comment_like + 1;
$sql_update = "UPDATE gaming_comments SET gaming_comment_like='$gaming_comment_like' WHERE gaming_comment_id='$commentId'";
$result_update = mysqli_query($conn, $sql_update);
exit();
}
}
here is the eventhandler that calling the likeButton function, which is in a php file:
<p><img src='like.png' class='like_button' onclick='likeButton(".$gaming_comment_id.", ".$user_id.");'>$gaming_comment_like</p>";