Php не обрабатывает форму

<?php echo $error; ?>
<form method="post" class="contact-form">
                                                            
                                                            <div class="row">
                                                                <div class="form-group col-md-6 col-lg-6 col-xl-6">
                                                                  <input type="text" name="name" class="form-control" placeholder="Name" required="required"/>

                                                                </div>
                                                                <div class="form-group col-md-6 col-lg-6 col-xl-6">
                                                                  <input type="email" name="email" class="form-control" placeholder="Email" required="required"/>
                
                                                                </div>
                                                            </div>                                                        
                                                            <div class="form-group">
                                                              <textarea name="message" class="form-control" rows="9" placeholder="Message" required="required"/></textarea>

                                                            </div>

                                                            
                                                                                                               
            <button type="submit" name="submit" id="" class="btn btn-primary">Submit</button>


                                                        </form>

$error = '';
$name = '';
$email = '';
$message = '';

function clean_text($string)
{
    $string = trim($string);
    $string = stripslashes($string);
    $string = htmlspecialchars($string);
    return $string;
}

if(isset($_POST["submit"]))
{
    if(empty($_POST["name"]))
    {
        $error .= '<p><label class="text-danger">Please Enter your Name</label></p>';
    }
    else
    {
        $name = clean_text($_POST["name"]);
        if(!preg_match("/^[a-zA-Z ]*$/",$name))
        {
            $error .= '<p><label class="text-danger">Only letters and white space allowed</label></p>';
        }
    }
    if(empty($_POST["email"]))
    {
        $error .= '<p><label class="text-danger">Please Enter your Email</label></p>';
    }
    else
    {
        $email = clean_text($_POST["email"]);
        if(!filter_var($email, FILTER_VALIDATE_EMAIL))
        {
            $error .= '<p><label class="text-danger">Invalid email format</label></p>';
        }
}
        

            
    if(empty($_POST["message"]))
    {
        $error .= '<p><label class="text-danger">Message is required</label></p>';
    }
    else
    {
        $message = clean_text($_POST["message"]);
    }
    if($error == '')
    {
        require 'class/class.phpmailer.php';
        $mail = new PHPMailer;
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