Add points to user shows no errors but doesn't add - php

Question

I need to add a option in the Admin page where a admin can Select a user and add points to them, however I write the name and how many points to add, enter it and it shows up with no errors but saying it has been successfully added, but the points have not been added to that user...
Here's my code for the page with the form:
if (empty($_POST) === false) {
$required_fields = array('username', 'add');
foreach($_POST as $key=>$value) {
if (empty($value) && in_array($key, $required_fields) === true) {
$errors[] = 'Fields marked with an asterisk are required';
break 1;
}
}
}
if (empty($errors) === false) {
if (user_exists($_POST['username']) === true) {
$errors[] = 'Sorry, the username \'' . $_POST['username'] . '\' doesn\'t exist';
}
}
?>
<?php
if (isset($_GET['success']) === true && empty($_GET['success']) === true) {
echo 'The points have succesfully been added to the user!';
} else {
if (empty($_POST) === false && empty($errors) === true) {
$addpoints = array(
'username' => $_POST['username'],
'add' => $_POST['add']
);
addpoints($addpoints);
header('Location: addthepoints352346.php?success');
exit();
} else if (empty($errors) === false) {
echo output_errors($errors);
}
?>
<h1>Admin Access Only</h1>
<p>Add points to a user</p>
<form action="" method="post">
<ul>
<li>
Username*:<br>
<input type="text" name="username">
</li>
<li>
How many points to add*:<br>
<input type="text" name="add">
</li>
<li>
<input type="submit" value="Add">
</li>
</ul>
</form>
<?php
}
include 'includes/overall/footer.php';
?>
And also another page with the function where it actually sends it to the mysql database:
function addpoints($addpoints) {
mysql_query("UPDATE `users` SET `points` = `points` + '$add' WHERE `username` = '$username'");
}
I literally have no idea what it is, to help I have added a couple of photos

Answer 1

update your function as follows.
function addpoints($addpoints) {
mysql_query("UPDATE users SET points = points +".$addpoints['add']." WHERE username = ".$addpoints['$username'].")";
}