I have completed the upgrade for your PHP store, ensuring full compliance with all your requirements. Technical implementation details: PhonePe Integration: I fixed the duplicate ID issues by implementing a unique merchantTransactionId logic (combining Order ID + Timestamp + Random seed). Real-time Cart: Used Vanilla JS (XMLHttpRequest) to ensure totals auto-update instantly without page refreshes, maintaining a lightweight and fast store. Product Colors: Added full support for color selection, which is now correctly passed and saved in the order record. Database & Code: Switched to PDO in db.php for better security and followed a "Clean Code" approach. All comments are in English for your review. Mobile Optimization: The quantity selector and checkout flow are 100% mobile-friendly. The attached ZIP includes: All 9 updated PHP/JS files. migration.sql to update your database tables. A README.txt with simple installation steps.