Ajax response always goes to success - php

Question

I have a form where the user has to enter their reservation id and last name. If these two values match in the database then I need to return the corresponding values from the database.
It looks like even if the wrong reservation id and name are put in, it treats it as success. The page reloads and display the foobar.
Here is my code
test06.php
<?php
$conn = mysqli_connect("","","","");
$reservation_id=$_POST['reservation_id'];
$guest_last_name=$_POST['guest_last_name'];
$stmt = $conn->prepare("SELECT reservation_id, guest_last_name, guest_full_name, unit_number, floor, key_sa
FROM reservations2
INNER JOIN guest ON (reservations2.reservation_id=guest.reservation_idg)
INNER JOIN unit USING (unit_id)
WHERE reservation_id=?
AND guest_last_name=?");
$stmt->bind_param("ss", $reservation_id, $guest_last_name);
$stmt->execute();
$stmt->bind_result($reservation_id, $guest_last_name,
$guest_full_name, $unit_number,
$floor, $key_sa);
if ($stmt->errno) {
die("Query failed to execute: " . $stmt->error);
}
if ($stmt->fetch()) {
echo json_encode(array("reservation_id" => $reservation_id,
"guest_last_name" => $guest_last_name,
"guest_full_name" => $guest_full_name,
"unit_number" => $unit_number,
"floor" => $floor,
"key_sa" => $key_sa));
} else {
$error="Not matching record";
echo json_encode($error);
}
$stmt->close();
?>
Inside HTML page
<p id='guest_full_name'></p>
<p id='unit_number'></p>
<p id='floor'></p>
<p id='error'></p>
<script>
function validateReservation(){
var reservation_id = document.getElementById("reservation_id").value;
var guest_last_name = document.getElementById("guest_last_name").value;
$.ajax({
type: 'POST',
url: 'test06.php',
// dataType: 'json',
data: {
'reservation_id': reservation_id,
'guest_last_name' : guest_last_name
},
success: function(json) {
var json = JSON.parse(json);
console.log(json);
$('#guest_full_name').html(json.guest_full_name);
$('#unit_number').html(json.unit_number);
$('#floor').html(json.floor);
$('#key_sa').html(json.key_sa);
},
error: function(err) {
console.log(err);
$("#error").html("Error!");
}
});
}

Answer 1

You have to send the status code. Echoing JSON will just give you a 200 response.
header('Content-Type: application/json');
http_response_code(500);
echo $json;
exit;
http://php.net/manual/en/function.http-response-code.php