Senior Software Engineer, Developer Platform

About the Opportunity

MoonPay is building a developer platform that allows partners to create native payment and crypto experiences directly inside their own products.

Historically, partners integrated MoonPay through a hosted widget and redirected users into a fixed MoonPay journey. We are now breaking the underlying system into reusable modules covering authentication, identity, KYC, quotes, payment methods and purchasing.

These capabilities are exposed through APIs, SDKs, embedded components, iframes and web views. Our goal is for a partner developer to integrate MoonPay's full capabilities without needing ongoing implementation support from our team.

This role owns the developer-facing layer between MoonPay's underlying payments infrastructure and the products our partners build. You will work across browsers, mobile applications and backend APIs to make complex financial workflows feel simple, predictable and native.

As a Senior Software Engineer, you will hold a hands-on technical position. You will build the platform itself rather than implementing one-off integrations for individual customers.

Build the developer platform

• Design and build APIs, SDKs and embedded components used by external developers.
• Turn MoonPay's existing authentication, identity, payment and purchasing capabilities into reusable platform modules.
• Develop secure browser and mobile integration patterns across iframes, web views and native applications.
• Create stable abstractions over complex payments, compliance and crypto infrastructure.
• Build reference applications, sandboxes and tooling that help developers move quickly from exploration to production.

Understand the integration deeply

• Own the complete developer journey, from obtaining credentials through to completing a live transaction.
• Design clear interfaces for sessions, authentication, quotes, payment methods, transaction state and errors.
• Handle the realities of browser and mobile environments, including cross-origin communication, redirects, storage restrictions and application lifecycle events.
• Develop consistent behaviour across web, iOS and Android integrations.
• Ensure integrations remain secure when operating inside products MoonPay does not control.

Make complex systems easy to use

• Design APIs and SDKs that are difficult to misuse and straightforward to debug.
• Establish clear versioning, compatibility and migration strategies.
• Build documentation around how developers actually use the platform rather than treating it as a secondary deliverable.
• Create useful errors, logs and observability so partners can resolve issues without contacting MoonPay.
• Reduce integration time and the amount of direct support required from engineering.

Operate payment-critical software

• Build systems where failures can prevent a customer from completing a purchase or leave a partner uncertain about transaction state.
• Design for retries, duplicate events, delayed responses and dependencies failing in unexpected ways.
• Implement idempotency, state recovery and graceful degradation across distributed payment flows.
• Measure API and SDK adoption, integration success, reliability and developer experience.
• Safely evolve the platform as MoonPay adds products, payment methods, regions and partners.

About You

Must-have experience and skills

• External developer products. You have built APIs, SDKs, embedded components or integration tooling used by third-party developers.
• Browser or mobile depth. You understand how browsers and mobile applications behave beneath the framework level, including sessions, storage, cross-origin communication and embedded experiences.
• JavaScript and TypeScript. You have strong language fundamentals and have built production client-side or SDK infrastructure.
• API and SDK design. You understand versioning, backwards compatibility, documentation, error design and safe migrations.
• Distributed systems. You build correctly when events arrive twice, late or out of order and when dependencies fail.
• Product judgement. You can turn complex platform capabilities into interfaces that developers can understand and adopt.
• Ownership. You have taken developer-facing software from design through launch, adoption and ongoing production support.

Nice-to-have experience

• Built payment APIs, checkout SDKs, embedded financial products or payment-method integrations.
• Built products similar to Stripe Elements, Stripe.js, Plaid Link or Braintree's client SDKs.
• Experience with secure iframes, web views, postMessage or cross-origin browser infrastructure.
• Developed SDKs across web, iOS or Android.
• Built sandboxes, test environments, reference applications or developer documentation.
• Experience with webhooks, idempotency, transaction state machines and payment orchestration.
• Worked on authentication, identity or KYC integrations.
• Familiarity with cryptocurrency, wallets or digital-asset products.
• Familiarity with our stack: TypeScript, Node.js, React, GCP, PostgreSQL, Redis and Kubernetes.

Benefits & Perks

• Competitive salary package
• Equity package, with all employees having ownership at MoonPay
• Pay-for-performance equity bonus
• Moonshot award: $250,000 equity grant for 20 employees a year
• Pension with employer contributions from day one
• Employee referral program: 10K in USDC for referrals
• Flexible time off and end-of-year company-wide Recharge Period
• Birthday leave and enhanced parental leave
• Hybrid working schedule, with fully remote options
• Commuter benefits and lunch credit on office days
• Private healthcare and Wellhub wellness membership
• Enterprise access to AI tools
• Home office setup allowance and remote working allowance
• Monthly product budget and zero-fee crypto transactions
• $1,000 annual training budget
• High Potential Program with structured development and mentorship
• Regular remote company offsites and hackathons
• (Ireland) Cycle to Work scheme
• (UK) EV Salary Sacrifice scheme