Uncaught PHPMailerPHPMailerException

I am using Xampp Server to do a send a message to an email.
I am using the PHP Mailer to do this

I ran into an error and i am not sure how to fix it , I would love some assistance if you have any

<html> 
<head>
  <title> Sending Email Using PHP </title>    
</head>
<body>
    
    <form method="post" action="">
        
        Please enter the email address <input type="email" name="to" placeholder="********@gmail.com">
        <br>
        
        Kindly enter the subject <input type="text" name="subject" placeholder = "Requesting all information">
        <br>
        
        Kindly enter the message <textarea name="message"> </textarea>
        <br><br>
        
        <input type="submit" value="Send">
    </form>
   
    <?php
    use PHPMailerPHPMailerException;
    use PHPMailerPHPMailerPHPMailer;
    use PHPMailerPHPMailerSMTP;
    
    require 'PHPMailer/src/Exception.php';
    require 'PHPMailer/src/PHPMailer.php';
    require 'PHPMailer/src/SMTP.php';
    require 'information.php'; //credentials for emails
    
    if($_SERVER["REQUEST_METHOD"] == "POST"){
    $to = $_POST["to"];
    $subject = $_POST["subject"];
    $message = $_POST["message"];
   
    
    $mail = new PHPMailer (true);
    $mail -> Subject = $subject;
    $mail -> Body = $message;
    $mail -> addAddress ($to);
    $mail -> AltBody = $message;
    $mail -> setFrom (SEND_FROM, SEND_FROM_NAME);
    $mail -> addReplyTo (REPLY_TO, REPLY_TO_NAME);
    $mail -> Host = MAILHOST;
    $mail -> Username = USERNAME;
    $mail -> Password = PASSWORD;
    $mail -> Port = 587;
    $mail -> isSMTP ();
    $mail -> SMTPAuth = true;
    $mail -> SMTPSecure = PHPMailer:: ENCRYPTION_STARTTLS;
    $mail -> IsHTML (true);
    $mail -> send ();
        
    if ($mail == true){
        
        echo "Message sent successfully";
    }
    
    else {
        
        echo "Message could not be sent";
    }
    }
    ?>
    </body>
</html>

This is the credentials for the emails called information.php

<?php

define ('MAILHOST', "smtp.gmail.com");
define ('USERNAME', "*******@gmail.com");
define ('SEND_FROM', "*******[email protected]");
define ('SEND_FROM_NAME', "**** *****");
define ('REPLY_TO', "student email");
define ('REPLY_TO_NAME', "*******");
define ('PASSWORD', "**%^&%*");

?>

The error was

Warning: Undefined array key “to” in (file name) on line 40

Fatal error: Uncaught PHPMailerPHPMailerException: Invalid address:
(to): in 1100 Stack trace: #0 :
PHPMailerPHPMailerPHPMailer->addOrEnqueueAnAddress(‘to’, NULL, ”)
#1(49): PHPMailerPHPMailerPHPMailer->addAddress(NULL) #2 {main} thrown in on line 1100