Experienced API Trading Platform Developer Needed (Lightspeed Connect)

I need help solving two critical challenges in an existing trading platform hosted on Amazon AWS: 1. Reliable order execution between the platform and Lightspeed Connect via API. 2. Accurate real-time Profit & Loss (P&L) calculation that matches the P&L shown in the Lightspeed Connect platform. This is an existing trading platform, so I'm looking for someone who has already worked on broker API integrations, real-time trading systems, and financial calculations. Requirements: * Proven experience with API trading platforms. * Experience integrating with broker APIs (Lightspeed Connect experience is a significant advantage). * Strong understanding of order execution, fills, positions, and real-time P&L calculations. * Experience with cloud-hosted applications (AWS). * Strong Python skills (FastAPI, async/await) — backend is built entirely in FastAPI. * Experience with WebSocket-based real-time market data feeds (we use Polygon.io). * Comfortable with SQLite for transactional/state data (orders, positions, trade history). * JavaScript experience (charting UI built on LightweightCharts). * Linux/Ubuntu server experience — deployed via systemd services on EC2. If you have successfully solved similar challenges before, I'd love to hear from you.