Senior Software Engineer – Back‑End

About Us
At sunday, we're redesigning the entire hospitality experience: not just payments.

With a phone and a simple QR scan, guests can access the menu, place their order, pay the bill, tip, and leave a review. We fine‑tune every touchpoint to deliver a seamless experience. Our latest innovation brings video into menus: not just visuals, but a way to build trust through transparency and spotlight the craft behind every dish.

Our mission goes beyond the guest experience. We build dedicated tools that empower teams, like our best‑in‑class payment terminal built for hospitality, saving servers valuable time. We also share real‑time guest reviews so teams can track satisfaction and improve their shift instantly. Hospitality is demanding: that's what drives us. It pushes us to move fast, think smart, and raise the bar every day. As our business grows, so do our teams. We're looking for people who can help us scale and bring structure without slowing us down.

About The Role
Join our
*3rd‑party POS Integrations
team. Our mission is to deliver a product that is
more stable and predictable than the upstream systems it relies on*
. You'll design and build the protective layer between sunday and a diverse ecosystem of POS vendors: implementing resilience, data quality, and observability so guests and merchants get a consistent experience regardless of vendor quirks or outages.

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.

Key Responsibilities

• 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 or equivalent), 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.

About You

• 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

*Nice to have*

• 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.

* Why this role matters
sunday is scaling across products, markets, and teams: and integrations are a force multiplier. This role ensures our experiences remain
fast, delightful, and resilient*
even when upstream systems aren't. You'll help shape how we build and scale the integration layer so we can grow with confidence.

Compensation, Perks & Benefits

• Competitive salary (75-90k) and equity
• Remote‑first friendly culture
• The chance to build products used by millions across the globe
• 100% health coverage for you and your children
• Free vacation policy
• Opportunity for significant impact in shaping innovative product development within a high‑growth environment

* Equal Opportunity*
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).