$_Get['id']; doesnt work

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PHP

hello this used to work before but since I have added a php mailer file to send an email it has stopped working. I want to be able to delete my record after the user has pressed on one of the two buttons. but right now I'm getting the error

Notice: Undefined index: id

how do I fix this?

full error

 Notice: Undefined index: id in C:\xampp\htdocs\bestelapp\delete.php on line 5
Error order record: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1

codes
these are the buttons that you press and then the system will send an email and delete the records

<?php 
include "navbar.php";
include "config.php";
?> 
<style>
    .container {
    font-family: Arial, Helvetica, sans-serif;
    font-size: 20px;
  }
    tr:first-of-type th:first-child 
    {
        border-top-left-radius: 10px; 
  
    }
  tr:first-of-type th:last-child{
    border-top-right-radius: 10px; 

  }
  
  /* tbody td:first-of-type th:last-child{
    border-bottom-right-radius: 10px;
  }
  tbody td:first-of-type th:last-child{
    border-bottom-left-radius: 10px;
  } */

</style>

<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-EVSTQN3/azprG1Anm3QDgpJLIm9Nao0Yz1ztcQTwFspd3yD65VohhpuuCOmLASjC" crossorigin="anonymous">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.2/css/all.min.css"/>
<div class="container">
<div class="table-responsive">
<table class="table table-dark table-hover" style=" width: 50%;   margin-left: auto; margin-right: auto; margin-top: 5%;">
  <thead>
    <tr>
      <th scope="col">order_id</th>
      <th scope="col">klant_id</th>
      <th scope="col">broodjes_ID</th>
      <th scope="col">klantnaam</th>
      <th scope="col">klant email</th>
      <th scope="col">Bevestigen?</th>
      <th scope="col">Afwijzen</th>
    </tr>
  </thead>
  <tbody>
  <?php
   $sql = "SELECT * FROM orders";
   $stmt = $conn->prepare($sql); 
   $stmt->execute();
   $result = $conn -> query($sql);
   $result = $stmt->get_result(); // get the mysqli result

      while($row = $result-> fetch_assoc()): ?>
      <tr>
        <td class="order_id"><?php echo $row["order_id"];?></td>
        <td class="klant_id"><?php echo $row["klant_id"];?></td>
        <!--Datum is eigenlijk meer voor de klant wanneer het kan worden opgehaald daar moet ene sorrt rekensom mee worden gemaakt-->
        <td class="broodjes_ID"><?php echo $row["broodjes_ID"];?></td>
        <td class="klantnaam"><?php echo $row["klantnaam"];?></td>
        <td class="klantemail"><?php echo $row["klantemail"];?></td>
        <td><form action="mail/bevestigordermail.php?order_id=<?php echo $row['order_id']; ?>" method="get">
              <button type="submit" class="btn btn-success" >class="fas fa-check" style="color: rgba(255, 255, 255, 1)"></button>
            </form>
        </td>
        <td><form action="mail/afwijzingordermail.php?order_id=<?php echo $row['order_id']; ?>" method="get">
              <button type="submit" class="btn btn-danger" >class="fas fa-times" style="color: rgba(255, 255, 255, 1)"></button>
            </form>
        </td>
      </tr>
      <?php endwhile; ?>
 </tbody>
</table>
</div>
</div>

the delete file: he can't find the id in here anymore

<?php

include "config.php"; // Using database connection file here
//werkt nog niet hij kan namelijk de id niet vinden dus dat moet nog gefixd worden
$id = $_GET['id'];
var_dump($id);
// sql to delete a record
$sql = "DELETE FROM orders WHERE order_id=?";
$stmt = $conn->prepare($sql); 
$stmt->bind_param('i', $id);
if ($stmt->execute()) {
  echo "order deleted successfully";
} else {
  echo "Error order record: " . $conn->error;
}

// //go back to index.php
    //  header('Location: index.php'); 
    // exit;

and lastly for (if it helps) my mail file
so when you press the button it will first fo right here and then to the delete script

<?php include "mailen.php"; 
include "../config.php";?>
<!-- moet ik heir prepared statements gebruiken?-->
<html>
   <!-- sending a mail -->
   <body>
      
      <?php
      //moet misschien nog in prepared statements maar eerst maar voor zorgen dat dit werkt
      //tijd plus 1 uur
         $newtime = date('H:i', time() + 3600);
         echo $newtime;
         $sql = "SELECT * FROM orders";
  
         $stmt = $conn->prepare($sql); 
         $stmt->execute();
         $result = $conn -> query($sql);
         $result = $stmt->get_result();
       
             while($row = $result-> fetch_assoc()){
                  $email = $row['klantemail'];
                  $klant = $row['klantnaam'];
                  $onderwerp = "Bestelling";
                  $bericht = "Geachte $klant, uw bestelling is bevestigd! U kunt uw order ophalen om $newtime";
                  mailen($email, $klant, $onderwerp, $bericht);
             }
             header("Location: ../delete.php");

      ?>
      
   </body>
</html>

What I have tried:

I have tried adding the id to my mail file but that doesn't do anything