Senior Full Stack Engineer

About The Role

We're hiring a Senior Full Stack Engineer to become the primary technical owner of String's platform.

You will build and own the technical systems that power String's cross-border payments infrastructure, from core application architecture and transaction workflows to cloud infrastructure, integrations, reliability and internal tooling.

This is a hands-on senior IC role with unusually broad ownership. You will write production code, troubleshoot incidents, make architecture decisions, integrate payment and financial partners and establish the engineering practices needed for the next stage of the company. As the engineering team grows, there is a clear opportunity to grow into broader technical leadership based on performance and company needs.

What you'll do

• Design, build and own the core application architecture, cloud infrastructure, databases, deployment pipelines, integrations and production environments
• Define and document system architecture, services, data flows, third-party dependencies and key technical risks
• Take day-to-day ownership of platform reliability, deployments, monitoring and production incident response
• Build, maintain and continuously improve reliable production systems as the platform scales
• Build new cross-border payment and international supplier-payment workflows
• Build and maintain APIs and integrations with banks, payment providers, liquidity partners, stablecoin infrastructure and other financial partners
• Develop internal operations, treasury, reconciliation and transaction-management tools
• Build and maintain customer-facing web applications and dashboards
• Design reliable transaction states, payment orchestration, webhooks, queues and asynchronous processing
• Improve observability through monitoring, logging, alerting and business-level workflow visibility
• Maintain CI/CD pipelines, cloud infrastructure, access controls and deployment processes
• Work closely with Operations, Compliance, Treasury and Commercial teams to turn business requirements into reliable systems
• Establish practical engineering standards for testing, documentation, security, code review and incident response
• Help interview and onboard additional engineers as the team grows

What we're looking for

• 5+ years of software engineering experience with meaningful experience owning production systems as a senior individual contributor
• Strong backend engineering skills with the ability to work effectively across the full stack
• Experience designing, building and operating production systems with significant end-to-end technical ownership
• Strong experience with APIs, relational databases, webhooks, queues and asynchronous or event-driven systems
• Experience with modern frontend frameworks such as React/Next.js or equivalent
• Experience with cloud infrastructure, CI/CD, containers, monitoring and production debugging
• Strong understanding of authentication, permissions, security, auditability and data integrity
• Ability to make sound technical decisions independently and communicate trade-offs clearly
• Comfort being the primary engineer initially and taking a requirement from business need through technical design, implementation, deployment and monitoring

Nice to have

• Experience building payments, fintech, banking, FX, trading, treasury, wallets or other transaction-intensive financial systems
• Experience with money movement, reconciliation, ledgers, idempotency and payment failure modes
• Experience integrating banks, PSPs, custody providers, exchanges or liquidity partners
• Blockchain-native experience is a strong plus, including stablecoins, wallet infrastructure, custody models, smart contracts, on-chain transaction flows or blockchain integrations
• Experience preparing systems for security or compliance audits
• Experience mentoring engineers or helping establish engineering standards in an early-stage team