Senior Stress Tester for High-Traffic Payment System

Looking for a senior freelancer to run stress tests on a high-traffic payment checkout system. Goal: simulate up to 80,000 users with concurrent orders and validate end-to-end stability. Tasks: - Design realistic load scenarios for checkout and payment flows - Simulate payment behaviors (success, declined, 3DS, timeouts) - Generate high concurrency with thousands of simultaneous requests - Identify bottlenecks across API, network, and payment provider - Validate idempotency and ensure no duplicate orders/payments - Test fallback and recovery flows (timeouts, retries, degraded network) - Analyze latency, error rates, and throughput under load - Validate behavior under sudden traffic spikes (burst load) - Deliver a clear report with issues, risks, and priorities - Suggest concrete improvements for scalability and resilience Requirements: - Strong experience with load testing tools (k6, JMeter, Gatling, etc.) - Experience with payment systems / high-concurrency checkouts - Ability to work with mocks or simulated payment providers - Practical mindset focused on finding real-world issues - Short, intensive engagement with immediate, actionable output.