mysqli_query(): Couldn't fetch mysqli

[rich_hemmo]

Hi guys I know this might be a repeated post, someone has looked at the code and they seem to think that it all look fine, but I'm getting this following message again

Warning: mysqli_query(): Couldn't fetch mysqli in C:\xampp\htdocs\submit-form.php on line 19
The following SQL Failed INSERT INTO 'users' ('firstname', 'lastname', 'username', 'confirmusername', 'password', 'confirmpassword', 'email' ,'confirmemail') VALUES ('richard', 'Hemmings', 'hemmo001', 'hemmo001', 'password', 'password', 'richardgwhemmings@msn.com' , 'richardgwhemmings@msn.com')

I just cant seem to see where I'm going wrong, at first there was a single quote missing from firstname' this I have now addressed, I've been woriking on this now for 2 weeks today!

Config.php

<?php 

$connection = mysqli_connect("localhost","root","","registration");

// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

mysqli_close($connection);
?>

submit-form.php

<?php
$connection = mysqli_connect("localhost", "root", "", "registration") or die("Error!!");
//select your database
//$b=mysql_select_db("Registration",$a);
$firstname=$_POST['firstname'];
$lastname=$_POST['lastname'];
$username=$_POST['username'];
$confirmusername=$_POST['confirmusername'];
$password=$_POST['password'];
$confirmpassword=$_POST['confirmpassword'];
$email=$_POST['email'];
$confirmemail=$_POST['confirmemail'];
//Database connection
require_once("config.php");

//mysql query to insert value to database
$query = "INSERT INTO `users` (`firstname`, `lastname`, `username`, `confirmusername`, `password`, `confirmpassword`, `email`, `confirmemail`) VALUES ('$firstname', '$lastname', '$username', '$confirmusername', '$password', '$confirmpassword', '$email', '$confirmemail')";
$result = mysqli_query($connection,$query);
//if value inserted successyully disply success message
if(!$result) {

    die("The following SQL Failed $query");
}
echo 'Registred successfully..!!</div>';
?>

Any help would be appreciated 

[mac_gyver]

the error is because you have closed the mysqli connection at the end of your config.php file.