Software Engineer – Back-End - POS Integrations

sunday is building the fastest, simplest way to pay in restaurants. With a quick scan of a QR code, diners can pay, tip, and leave in about 10 seconds. We believe great products should feel obvious, not complicated, and we focus relentlessly on keeping things simple while earning trust from restaurants and guests at every interaction. Today, sunday powers payments in thousands of restaurants across the US, UK, and France, helping operators turn tables faster, increase tips, and unlock valuable insights. We push ourselves to go beyond what’s expected, building with ownership, moving fast, and scaling with ambition as we tackle our biggest growth opportunity in the US.

Join our 3rd-party POS Integrations team. Our mission is to bring consistency and reliability to one of the most fragmented software ecosystems in the world. Restaurants rely on hundreds of different POS systems and each have its own specificities, limitations, and operational challenges. Your role will be to help abstract that complexity away and build the platform layer that standardizes how sunday interacts with the entire ecosystem.

While you'll focus on back-end systems, you're comfortable venturing across the stack when needed: making small changes to front-end flows and touching infrastructure to ship end-to-end improvements.

• Elevate stability and cohesion across integrations to deliver a unified, high-quality experience for merchants and guests.
• Lead architectural decisions for scalability, resilience, and maintainability (e.g., idempotency, retries with backoff, circuit breakers, DLQs, backpressure, rate limiting, graceful degradation).
• Pitch in beyond back-end when needed: small UI fixes in our admin/ops panels and light infra changes (pipelines, configs, IaC) to unblock delivery.
• Design clear API contracts and schemas (REST/gRPC) and evolve them safely over time with versioning and ADRs.
• Raise the bar on observability: define SLOs/error budgets, improve logs/traces/metrics (Datadog), add synthetic checks, and build actionable dashboards/runbooks.
• Own data correctness and reconciliation across eventually consistent, distributed systems (outbox/inbox patterns, deduplication, replays, CDC, re-sync jobs).
• Debug complex incidents end-to-end across our services and third-party vendors; drive root-cause analysis and long-term fixes; analyze and solve memory leaks and related issues.
• Partner with Product, Support, and Integrations/CS teams to turn real-world issues and merchant feedback into roadmap value.
• Mentor engineers and contribute to shared tooling, documentation, and Architecture Decision Records (ADRs).
• Ship fast, safely using CI/CD, feature flags, canaries, and incremental rollouts.

• Outcome-driven and comfortable in fast, evolving contexts: you ship results, not just code.
• End-to-end ownership: shaping problems, delivering clean solutions, and ensuring smooth production operations.
• Lead by example: mentoring, improving practices, and aligning teams on a clear architecture and standards.
• Strong back-end proficiency with Java/Kotlin/Spring and scalable integration architectures.
• Fluent in testing strategies for integrations: unit/integration and non-prod vendor mocks/sandboxes.
• Skilled at performance analysis and observability-driven debugging across distributed systems.
• Comfortable making small front-end changes (React) and light infra adjustments (CI/CD, Helm/Terraform/config) to ship holistic improvements.
• Clear communicator in writing and in real time, and you know when a quick call or pairing session beats a long thread.
• Experience with POS ecosystems (e.g., Toast, Lightspeed, Oracle Micros, NCR Aloha, L'Addition, TISSL, etc.).
• Event-driven systems (Kafka/RabbitMQ), stream/batch data flows, and stateful workflows (saga/orchestration).
• Security for integrations: OAuth2/mTLS/API keys, secrets management, webhook signature validation.
• Practical knowledge of caching, rate limiting, TTLs, and consistency strategies to balance latency and correctness.

🐾 Steps in our Recruitment Process

Thank you for taking the time to apply, and looking forward to getting to know you!

sunday is an equal opportunity employer and does not discriminate and all qualified applicants will receive consideration for employment without regard to race, creed, color, sex, affectional or sexual orientation, gender identity or expression, gender, ethnicity, religion, national origin, ancestry, nationality, age, disability, marital status, veteran status, genetic information, or on any other basis prohibited by law (except where an attribute is a bona fide occupational qualification).