Manual Code Refactoring, Bug Fixing, and Security Hardening of a PHP/Twig SMM Panel Script

I have a complete PHP-based SMM Panel script that uses Twig for templating, PDO for database connections, and PHPMailer. However, the script has a lot of internal coding flaws, broken/half-written logic, duplicate conditions, and bad structure due to multiple previous edits... (Budget: ₹1000 - ₹2000 INR, Jobs: HTML, JavaScript, MySQL, PHP, Website Design)