How can I insert a Data inputted in a textbox from an onclick Alert input event into DataBase

UI

code for the PHP Submit Script

if (isset($_POST['rejectreason'])){
$Note = $_POST['rejection_reason'];
$whyreject = 'Rejection_Reason-'.$Note;

 $sql = "UPDATE requestitem SET requestitem_UsefulNote='$whyreject' ";
 $query = $dbh->prepare($sql);
 if ($query->execute()){
      $success="Rejection Confirmed Successfully and Reason Sent.";          
}else {
      $error="Sorry, Rejection Failed, Try again Later.";
      }
}

code for the cancel button

 <input type="hidden" id="rjctrsn-data" href="" name="rejection_reason">	

<a type="submit" name="rejectreason" onclick="document.getElementById('rjctrsn-data').value = prompt('Are you sure you want to Reject this Item ! :', 'Please State Reason for Rection');"
value="" class="btn btn-xs delete-record" data-id="0">
<span style="font-size:25px" class="glyphicon glyphicon-remove text-danger" style="color:red"></span>
</a>

Trigger the onclick alert input event and get the user input

<form action="submit_script.php" method="post">
  <button type="button" onclick="showRejectionReasonAlert()">Reject</button>
</form>



<script>
function showRejectionReasonAlert() {
  var rejectionReason = prompt("Please enter the rejection reason:");
  if (rejectionReason != null) {
    document.getElementById("rjctrsn-data").value = rejectionReason;
    document.getElementById("yourFormId").submit();
  }
}
</script>

Ensure to properly set up your database connection before executing the SQL.

<?php

if (isset($_POST['rejection_reason']) && !empty($_POST['rejection_reason'])) {
    $Note = $_POST['rejection_reason'];
    $whyreject = 'Rejection_Reason-' . $Note;

    $sql = "UPDATE requestitem SET requestitem_UsefulNote=:whyreject";
    $query = $dbh->prepare($sql);
    $query->bindParam(':whyreject', $whyreject);

    if ($query->execute()) {
        $success = "Rejection Confirmed Successfully and Reason Sent.";
    } else {
        $error = "Sorry, Rejection Failed, Try again Later.";
    }
}