Move uplaod file false result? [closed]

I try to accept a file using php:

<?php

if (isset($_FILES["file"])) {

  $uploaddir = '/';
  $uploadfile = $uploaddir . basename($_FILES['file']['name']);


  if (move_uploaded_file($_FILES['file']['tmp_name'], $uploadfile)) {
    echo "File is valid, and was successfully uploaded.n";
  } else {
    echo "Error";
  }
}

I send Postman request as POST form-data: file: Filename.

Why I always get echo "Error";?