Zalando - iOS Payment SDK

At Zalando SE, I worked as a Senior iOS SDK Engineer focused on building and maintaining the Payment SDK that powered Zalando’s shopping ecosystem. The SDK was designed in Swift, with modular boundaries and a clean public API to support multiple client applications across Zalando’s product portfolio. The goal was to deliver a fast, stable, and privacy-compliant checkout experience that could scale safely under heavy user load. My work included designing the SDK structure, improving latency, and ensuring smooth integration for internal teams. The SDK handled millions of monthly transactions and became a critical part of Zalando’s commerce infrastructure. Key Contributions: - Co-designed a multi-client Payment SDK in Swift, enforcing strict module boundaries, dependency injection, and public API contracts for long-term maintainability. - Built asynchronous pipelines using RxSwift and GCD to meet checkout latency budgets. - Improved checkout latency by ~15% through targeted performance profiling and optimization. - Strengthened error handling and observability, enabling safer rollouts across five consumer apps. - Implemented an offline-first “add-to-cart” flow, allowing users to queue purchases under unstable networks. - Established integration and UI test suites with CI release gates and telemetry dashboards to detect regressions early. - Supported 3M+ monthly transactions through API hardening, network reliability improvements, and testing. - Collaborated closely with Security, Backend, and Design teams to ensure compliance, performance, and a consistent user experience.