Почему сообщения не отправляются, php

Question

Всем привет, делаю форум. Использую ajax для отправки сообщений без перезагрузки, и написал такой код: JS:

```
$(document).on('load', function() {
    $('#form-bt').click(function(){
        var comment = $("#comment").val();
        var username = $("#username").val();
        $.ajax({
            url: 'index.php',
            type: 'POST',
            dataType: 'json',
            data: {
                comment: comment,
                username: username,
            },
            success: function(data){
                alert("Наконец-то всё получилось!");
            },
            error: function(){
                console.log('ERROR');
            }
        })
    })
})
``` 

PHP:

```
 <?php
    include 'index.html';
    $connect = new PDO ("mysql:host=localhost; dbname=forum;charset=UTF8", 'root', 'root');
    if (isset($_POST['username'])){
        $username = $_POST['username'];
        $comment = $_POST['comment'];
        $date = date('H:i:s');
        $query = $connect->query("INSERT INTO forum.comments (username, comment, data) VALUES ('$username', '$comment', '$date')");
    }
$comments = $connect-&gt;query(&quot;SELECT * FROM forum.comments ORDER BY data DESC&quot;);
$comments = $comments-&gt;fetchAll(PDO::FETCH_ASSOC);
if ($comments){
    foreach($comments as $comment){

        echo &quot;{$comment['data']} . {$comment['username']}&quot;;
        echo &quot;&lt;br&gt;&quot;;
        echo &quot;{$comment['comment']}&quot;;
        echo &quot;&lt;br&gt;&quot;;

    }
}else{
    echo &quot;Пока нет ни одного комментария :(&quot;;
}

?>
</code></pre>
<p>HTML:</p>
<pre><code>```
&lt;!DOCTYPE html&gt;
&lt;html lang=&quot;en&quot;&gt;
&lt;head&gt;
    &lt;meta charset=&quot;UTF-8&quot;&gt;
    &lt;meta http-equiv=&quot;X-UA-Compatible&quot; content=&quot;IE=edge&quot;&gt;
    &lt;meta name=&quot;viewport&quot; content=&quot;width=device-width, initial-scale=1.0&quot;&gt;
    &lt;title&gt;Document&lt;/title&gt;
    &lt;link rel=&quot;stylesheet&quot; href=&quot;style.css&quot;&gt;
    &lt;style&gt;
        body{
    font-family:'Franklin Gothic Medium', 'Arial Narrow', Arial, sans-serif;
    box-sizing: border-box;
}
* {
    box-sizing: border-box;
}
input, textarea{
    position: relative;
    width: 100%;
    margin: 5px;
    bottom: 0px;
}
form{
    display: flex;
    flex-direction: column;
}
p{
    font-size: 1vw;
    color: #357a6a;
}
.block-comment, .block{
    margin: 2vw 2vw 2vw 2vw;
    font-weight: bold;
    overflow-y: scroll;
}
.block{
    max-height: 30vw;
}
hr{
    background-color: #414b0c;
    margin: 2vw 2vw 2vw 2vw;
    height: 1%;
}
.line{
    width: 100%;
    height: 0.2vw;
    margin-top: 0.5vw;
    background-color: #414b0c;
}
h2{
    font-family: 'Franklin Gothic Medium', 'Arial Narrow', Arial, sans-serif; 
    margin: 2vw 2vw 2vw 2vw;
}
@font-face {
    font-family: &quot;Vinnytsia City&quot;; 
    src: url(&quot;https://fonts-online.ru/fonts/vinnytsia-city&quot;) format(&quot;truetype&quot;); 
    font-style: normal; 
    font-weight: normal; 
    font-family: Vinnytsia City; /* Гарнитура шрифта */
    src: url(https://fonts-online.ru/fonts/vinnytsia-city); /* Путь к файлу со шрифтом */
} 
    &lt;/style&gt;
&lt;/head&gt;
&lt;body&gt;

&lt;h2&gt;Форум&lt;/h2&gt;

&lt;div class=&quot;block&quot;&gt;
    &lt;form action=&quot;&quot; method=&quot;POST&quot; id=&quot;form&quot;&gt;
        &lt;div class=&quot;block-comment&quot;&gt;
            &lt;input type=&quot;text&quot; id=&quot;username&quot; name=&quot;username&quot; class=&quot;r&quot; placeholder=&quot;Ваше имя&quot; required&gt;
            &lt;textarea name=&quot;comment&quot; id=&quot;comment&quot; cols=&quot;10&quot; rows=&quot;5&quot; class=&quot;r&quot; placeholder=&quot;Ваш комментарий&quot; required&gt;&lt;/textarea&gt;
            &lt;input type=&quot;button&quot; id=&quot;form-bt&quot; value=&quot;отправить&quot;&gt;
        &lt;/div&gt;
    &lt;/form&gt;
&lt;/div&gt;
&lt;script src=&quot;jquery-3.6.0.min.js&quot;&gt;&lt;/script&gt;
&lt;script src=&quot;form.js&quot;&gt;&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;

При этом, не используя submit. Пожалуйста, помогите.