PHP Script Loading Forever - php

Question

This is not a duplicate of Maximum execution time in phpMyadmin; this has nothing to do with phpmyadmin.
On my site, there is a form which sends POST data to a PHP script and loads a new page. When you submit the form, the page loads forever and then results in:
The XXX.XXX page isn’t working XXX.XXX is currently unable to handle
this request. HTTP ERROR 500
I thought it may be a traffic issue so I upgraded my hosting SSD and made the website only available to me to test it, but the problem still persisted. Here is my script:
<?php
$used_file = 'used.txt';
$codes_file = 'codes.txt';
# Generates a random unused code from the code file
function genCode() {
global $used_file, $codes_file;
$codes = file_get_contents($codes_file);
$codes = explode("\n", $codes);
$used = file_get_contents($used_file);
$used = explode("\n", $used);
foreach($codes as $code) {
if(!in_array($code, $used))
return $code;
}
}
# Generate error string from error code
function getError($err) {
switch($err) {
case 1: return 'No submit';
case 2: return 'Wrong password';
case 3: return 'No password';
}
}
# Adds generated code to the 'used' codes file
function append_used($code) {
global $used_file, $codes_file;
$str = $code . '\n';
file_put_contents($used_file, $str, FILE_APPEND);
}
# Get user's IP (for cookie handling)
function getIP() {
if (!empty($_SERVER['HTTP_CLIENT_IP'])) {
$ip = $_SERVER['HTTP_CLIENT_IP'];
} elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
$ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
} else {
$ip = $_SERVER['REMOTE_ADDR'];
}
return $ip;
}
# Cookie handling
# Set a cookie for how many times the form has been submitted by user
$used = 0;
if(isset($_COOKIE['used_twice'])) {
$used = 3;
}
if(isset($_COOKIE['used_once']) && !isset($_COOKIE['used_twice'])) {
setcookie('used_twice', getIP(), time()+18000);
$used = 2;
}
if(!isset($_COOKIE['used_once'])) {
setcookie('used_once', getIP());
$used = 1;
}
# Check if all the POST data is correct
$password = $_POST['inputPassword'];
$submit = $_POST['submit'];
if(isset($password)) {
if($password == 'test123') {
if(isset($submit)) {
$code = genCode();
}
else
$err = 1;
} else
$err = 2;
} else
$err = 3;
# Now generate the new page
include 'web_functions.php';
getHead('Generated', 'Generated code');
getBody('Generated code');
?>
<img src="goback.png"></img>
<h2>Code Generated</h2>
<br/>
<?php
if(!isset($err) && isset($thecode) && $used == 1) {
?>
<center>
<div class="bs-component">
<div class="alert alert-dismissible alert-success">
<p>Your code is: </p> <strong> <?php echo $thecode; append_used($thecode); ?> </strong>
</div>
</div>
</div>
</center>
<?php
} elseif(isset($err)) {
?>
<center>
<div class="bs-component">
<div class="alert alert-dismissible alert-danger">
<p>There was an error:</p> <strong><?php echo getError($err); ?></strong>
</div>
</div>
</div>
</center>
<?php
} elseif(!isset($err) && $used != 1){
?>
<center>
<div class="bs-component">
<div class="alert alert-dismissable alert-danger">
<p>You can only use the code generator once every 5 hours. Please try again later.</p>
</div>
</div>
</div>
</center>
<?php } else { ?>
<div class="bs-component">
<div class="alert alert-dismissable alert-danger">
<p>There was an unexpected error. Please try again.</p>
</div>
</div>
</div>
<?php } ?>
<br/>
<br/>
<br/>
<?php closeTags();
getFooter(); ?>
</div>
</div>
</div>
</div>
What could be causing this issue?
Edit: The error log says:
PHP Fatal error: Maximum execution time of 60 seconds exceeded on line 13
Line 13 is within the foreach loop.