Issues with Electronic Signature Scipt

I am trying to create a script to upload an electronic signature to the a customers record but keep getting ID not specified error message 🙁

This is what I have come up with so far.

Code

if (isset($_GET['id'])) {

    $stmt = $pdo->prepare('SELECT * FROM contacts WHERE id = ?');
    $stmt->execute([$_GET['id']]);
    $contact = $stmt->fetch(PDO::FETCH_ASSOC);

    $stmt = $pdo->prepare('SELECT id,username FROM accounts');
    $stmt->execute();
    $all_account_info = $stmt->fetchAll(PDO::FETCH_ASSOC);

    $folderPath = "upload/";
    $image_parts = explode(";base64,", $_POST['signature']);
    $image_type_aux = explode("image/", $image_parts[0]);

    $image_type = $image_type_aux[1];

    $image_base64 = base64_decode($image_parts[1]);

    $file = $folderPath . $name . "_" . uniqid() . '.' . $image_type;

    file_put_contents($file, $image_base64);

    if(isset($_POST['name']) == null || isset($_POST['signature_img'])){
        $msg    =   '';
    }else{
        $id = isset($_POST['id']) && !empty($_POST['id']) && $_POST['id'] != 'auto' ? $_POST['id'] : auto;
        $stmt = $pdo->prepare('INSERT INTO skreading1 VALUES (?, ?, ?, ?)');
        $result = $stmt->execute([$id, $_GET['id'], $_POST['$name'], $_POST['$file']]);
        $msg    =   "Signature has been recorded.";

    }

    if (!$contact) {
        exit('Help');
    }
} else {
    exit('No ID specified!');
}

?>

Form

                        <form action="add-sig.php" method="post">
                            <h1>Signature Pad</h1>
                            <div class="col-md-12">
                                <label class="form-label" for="name">Name</label> <input class="form-control" id="name" name="name" required="" type="text">
                            </div>
                            <div class="col-md-12">
                                <label class="" for="">Signature:</label><br>
                                <div id="sig"></div><br>
                                <textarea id="signature64" name="signature" style="display: none"></textarea>
                                <div class="col-12">
                                    <button class="btn btn-sm btn-warning" id="clear">&#x232B;Clear Signature</button>
                                </div>
                            </div><br>
                            <button class="btn btn-success" name="submit" type="submit">Submit</button>
                        </form>
                    </div>

Database

  `id` int(11) NOT NULL,
  `client_id` int(11) NOT NULL,
  `name` varchar(100) NOT NULL,
  `signature_img` varchar(255) NOT NULL

It loads the ID when clicking add signature and the address link looks something like .php?id=29 from the clients record.

When I am in the clients record, I would like to be able to view the signature on their record.

The form converts the signature into an image file.