One of the major challenges we faced was integrating accurate, real-time market data without introducing delays or performance issues. The paper trading feature was also complex to develop, as we had to simulate real trades and accurately track gains and losses without actual money. Handling large datasets and interactive visualizations efficiently was another hurdle, as we needed to ensure the app remained responsive. Designing a user interface that balances simplicity for beginners and depth for experienced traders was tricky, as it had to support strategy creation without overwhelming users. Ensuring data security throughout the platform, particularly during paper trading, was also a priority. We also had to build a robust backtesting system that could handle multiple trading strategies on historical data. Finally, deployment posed challenges in ensuring the app scaled well and worked seamlessly across different devices and platforms.