I need a seasoned full-stack developer to architect and build a payment gateway that works flawlessly on both my web application and its native mobile companions. The system must authorise and settle transactions in USD, EUR and GBP from day one, while remaining flexible enough to add further currencies with minimal code changes. Core scope You will handle everything from the database schema and secure APIs to the responsive checkout UI that drops into the website and the lightweight mobile components that plug straight into iOS and Android. Strong knowledge of tokenisation, PCI-DSS practices, 3-D Secure, fraud-screening hooks and webhook-based event reporting is essential because compliance and reliability sit at the heart of this project. Key deliverables • Fully documented REST (or GraphQL) API • Hosted checkout page and embeddable widget for the web app • Mobile-ready flow (either native SDK wrappers or a secure webview solution) • Admin dashboard with transaction search, refund handling and basic analytics • Automated test suite and deployment scripts Acceptance criteria The finished gateway must process live card payments in the three required currencies, pass PCI scans, and return deterministic results in sandbox mode so I can run integration tests in CI/CD. To apply Point me to previous payment, fintech or similarly complex back-end projects you’ve delivered—real, production-level work carries the most weight. A concise repo or demo link that shows secure handling of sensitive data will help me shortlist quickly.