Web Push Panel Post URL Redirection

I do not know much about coding, but recently I got a self-hosted web-push panel made for my website by a developer, he also gave a plugin for my WordPress website. The admin panel works fine, there is something wrong with it, maybe he didn’t fix it on purpose

Like when I send a notification of a post from my WordPress website, the notification goes but when the subscriber clicks on that post, it gets redirected to a different URL when I checked the files of the panel, I found a file called link.php

There is a code in that file in which that Redirect URL is set as if I set that URL to google.com, then after clicking on my post, the user landed on google.com and not on my post and the developer did the same With many things, I was given a script like unlimited subscribers, but the notification goes to only 10k people.

Now I am not having any contact with that developer so how can I fix this redirection problem please give any suggestion

link.php code

<?php

const BASE_PATH = __DIR__;
require_once BASE_PATH.'/system/init.php';

$linkId = (isset($_GET['linkId']) && !empty(trim($_GET['linkId'])))? SQLSecure(base64_decode($_GET['linkId'])) : '0';

$linkQuery = $DB->query("SELECT * FROM `links` WHERE `id`='{$linkId}'");
if($linkQuery->num_rows > 0){
    $LinkData = $linkQuery->fetch_assoc();
    $DB->query("UPDATE `links` SET `clicks`=`clicks`+1 WHERE `id` = '{$LinkData['id']}'");
    redirect($LinkData['full_link']);
}
redirect('https://google.com');

?> 

the other file code, mentioned in the link.php file system/init.php

<?php

ini_set('max_execution_time', 0);
ini_set('session.cookie_httponly',1);
ini_set('session.use_only_cookies',1);
ini_set('session.cookie_secure', 1);
ini_set('session.cookie_samesite', 'Strict');
session_start();

require_once BASE_PATH.'/config.php';
require_once __DIR__.'/core/database.php';
require_once __DIR__.'/core/functions.php';
require_once __DIR__.'/core/app-start.php';