Senior Software Engineer, Developer Platform

About the role

MoonPay is building a developer platform that lets partners create native payment and crypto experiences inside their own products, moving beyond a hosted widget to reusable modules for authentication, identity, KYC, quotes, payment methods and purchasing. This role owns the developer-facing layer between MoonPay's underlying payments infrastructure and the products its partners build, working across browsers, mobile apps and backend APIs. It is a hands-on, senior engineering position focused on building the platform itself.

Key responsibilities

• Design and build APIs, SDKs and embedded components used by external developers.
• Turn existing authentication, identity, payment and purchasing capabilities into reusable platform modules.
• Develop secure browser and mobile integration patterns across iframes, web views and native apps.
• Create stable abstractions over complex payments, compliance and crypto infrastructure.
• Build reference applications, sandboxes and tooling that help developers move from exploration to production.
• Own the complete developer journey, from credentials to a live transaction, and design clear interfaces for sessions, authentication, quotes, payment methods, transaction state and errors.
• Handle browser and mobile realities such as cross-origin communication, redirects, storage restrictions and application lifecycle events, ensuring consistent behaviour across web, iOS and Android.
• Keep integrations secure in products MoonPay does not control, and design APIs and SDKs that are easy to debug and versioned with clear migration paths.
• Build documentation, errors, logs and observability so partners can resolve issues without contacting engineering.
• Design for retries, duplicate events, delayed responses and failed dependencies, with idempotency, state recovery and graceful degradation.
• Measure API and SDK adoption, integration success, reliability and developer experience.

Required profile

• Experience building APIs, SDKs, embedded components or integration tooling used by third-party developers.
• Understanding of how browsers and mobile apps behave under the hood, including sessions, storage and cross-origin communication.
• Strong JavaScript and TypeScript fundamentals, with production client-side or SDK infrastructure.
• Knowledge of API and SDK design: versioning, backwards compatibility, documentation, error design and safe migrations.
• Experience with distributed systems, handling events arriving twice, late or out of order and failing dependencies.
• Ability to turn complex platform capabilities into interfaces developers can adopt, and ownership of developer-facing software from design through launch and production support.

Nice to have

• Prior payment APIs, checkout SDKs, embedded financial products or payment-method integrations.
• Products like Stripe Elements, Stripe.js, Plaid Link or Braintree's client SDKs.
• Secure iframes, web views, postMessage or cross-origin infrastructure; SDKs across web, iOS or Android.
• Sandboxes, test environments, reference apps or developer documentation.
• Webhooks, idempotency, transaction state machines, payment orchestration, authentication, identity or KYC integrations.
• Cryptocurrency, wallets or digital-asset products.
• Familiarity with the stack: TypeScript, Node.js, React, GCP, PostgreSQL, Redis and Kubernetes.