if ($post['status'] == 'success') {
$merchant_oid = $conn->real_escape_string($post['merchant_oid']);
$sql = "UPDATE orders SET STATUS = 'ONAYLANDI' WHERE ORDER_NUMBER = '$merchant_oid'";
if ($conn->query($sql) === TRUE) {
echo "OK";
exit();

} else {
echo "Error: " . $sql . "<br>" . $conn->error;
}