GET http://localhost/oramexhomes/backend/index.php 404 (Not Found)

1. [Violation] 'submit' handler took 3501ms jquery.min.js:2

2. GET http://localhost/oramexhomes/backend/index.php 404 (Not Found)

I get these two errors in my console.log when i try to post data using query ajax post to my php file.

my folder structure is oramexhomes/index.php for my index page and all frontend pages and codes for my backend codes and files = oramexhomes/backend/authController.php I am trying to post using jquery/ajax to backend

<script>
$("#agentregistration").submit(function(esignup){
esignup.preventDefault();
validatesurname();
validatefirstname();
validatephonenumber();


if (
surnameError == true &&
firstnameError == true &&
phonenumberError == true &&
emailError == true
) {
      
$.ajax({
  type: "POST",
  url: "backend/authController.php",
  data: $("#agentregistration").serialize(),
  dataType : "json",
  
  success : function(response){
    console.log(response);
    if(response.status){
      toastr.success(response.message);
      $('#agentregistration')[0].reset();
      $('#registrationmodel').modal('hide');
    }else {
      toastr.error(response.message);
    }
}

});
return true;
}
});
</script>

oramexhomes/backend/authController.php

 if (isset($_POST['agentform'])) {
    
    
        $surname = $_POST['surname'];
        $firstname = $_POST['firstname'];
        
    
    if (strlen($surname) < 1) {
         $_SESSION['error']      = "Please, add surname";
         header("Location:index.php");
        
         return;
    }

    if (strlen($firstname) < 1) {
        $_SESSION['error']   = '<div class="alert alert-danger">"Please, add your first name"</div>';
        header("Location:index.php");
        
        return;
    }
$sql = "INSERT INTO agent (agent_id, Surname, First_name, Other_names, Email, Password, Phone_number, Refeeral_id, verified, token)
        VALUES (:agentid, :surname, :firstname, :othernames, :email, :password, :phonenumber, :refeeralid, :verified, :token)";
        $stmt = $pdo->prepare($sql);
        $stmt->execute(array(
        ':agentid' =>  $agentid,
        ':surname' => $_POST['surname'],

$success = '<div class="alert alert-success"> Thank you for registering with Oramex Property. To continue, please sign in to your email account and click on 
                        the verification link we just emailed you at <strong>'.$_SESSION['email'].'</strong></div>';
        $response = array('status' => true, 'message' => $success);
         header("Location:index.php");
        return;
        }else 
         {
            $response = array('status' => false, 'message' => $_SESSION['error']);
    } 
echo json_encode($response);
}

1. I expect at least console.log to give me list of data that is posted but it doesnt.
2. data is not inserted in the database.
3. before toastr.error shows message from severside but now it does not.