Backend Engineer – API Integrationen, Connectoren, Worker/Jobs, Mailer Service, QA

Accountabilities

• • Build and maintain production-ready API integrations and connectors, prioritizing Box and HubSpot, followed by Microsoft Graph, Asana, and billing-related systems.
  • Implement reliable authentication and integration patterns using OAuth, webhooks, pagination, rate limits, retries, and robust error handling.
  • Design and develop queue-driven, stateful, and replayable workers and background jobs.
  • Build and maintain a mailer service supporting PDF attachments, structured logging, retry mechanisms, delivery checks, and deduplication/idempotency.
  • Design database schemas and implement clean, reliable migrations using PostgreSQL or comparable technologies.
  • Implement audit events and persistent traceability mechanisms, including correlation IDs and observability across distributed processes.
  • Develop comprehensive QA coverage, including contract tests, integration tests, and end-to-end regression testing for critical workflows such as document delivery and deadline-related processes.
  • Use Docker, queue/eventing technologies, and observability practices to support reliable deployment and operation of backend services.
  • Proactively identify failure modes and strengthen systems against timeouts, webhook failures, rate limiting, retries, duplicate events, and other production scenarios.

  Requirements

  • Strong professional track record in backend engineering, with proficiency in Python, Node.js, Go, or a comparable backend technology.
  • Proven experience building and maintaining production API integrations, including OAuth, webhooks, pagination, rate limits, authentication, and error handling.
  • Solid understanding of relational databases, schema design, data persistence, and safe database migrations.
  • Strong testing mindset with experience implementing contract, integration, unit, and/or end-to-end tests.
  • Experience developing asynchronous, queue-based, or event-driven systems and background workers.
  • Understanding of reliability engineering principles, including idempotency, retries, replayability, deduplication, observability, and failure-mode analysis.
  • Experience working with Docker and modern backend development and deployment workflows.
  • Familiarity with PostgreSQL, queue/eventing systems, and application monitoring or observability tools.
  • Strong problem-solving skills and the ability to design systems that remain reliable outside of ideal or “happy path” scenarios.
  • Ability to work independently, take ownership of technical deliverables, and communicate clearly in a remote project environment.
  • Availability to work remotely, ideally aligned with Central European Time (CET) or European working hours.
  • Freelance or project-based experience is suitable for this engagement.

  Benefits

  • 100% remote working arrangement.
  • Flexible project-based engagement with workload agreed upon according to availability and project needs.
  • Full-time or part-time engagement options.
  • Freelance contract structure.
  • Opportunity to work on technically challenging API integrations, worker systems, messaging infrastructure, and QA automation.
  • Significant ownership over backend architecture, implementation, reliability, and delivery.
  • Opportunity to start as soon as possible.
  • Collaboration within an international and digitally focused professional environment.