Senior Backend Engineer (Kotlin / Java)

Fourthwall is a product company with offices in Los Angeles and Poznań, serving creators, brands, and startups who run shops, memberships, and donations on their own domains. They have over 500,000 creatives and companies as users, including notable investors and clients. Fourthwall acts as the merchant of record, handling product manufacturing, shipping, ecommerce platform, customer support, and taxes in one integrated Kotlin codebase service. The company embraces remote work within Poland and has a modern technology stack including Kotlin, Spring Boot, jOOQ on PostgreSQL, Arrow, and Google Cloud.

• Experience in production backend development with Kotlin or Java and Spring framework.
• Strong knowledge of SQL and understanding of ORM abstractions.
• Ability to decide when to use return types like Either or Result versus exceptions for error handling.
• Experience integrating third-party APIs end-to-end, including handling contract, retries, and idempotency.
• Understanding of performance and failure modes for queries, HTTP calls, or background jobs.
• Demonstrated experience shipping features and analyzing their impact on users or revenue.
• Ability to adapt requirements when needed with clear reasoning.
• Experience working outside usual areas, such as data pulls or infrastructure modules.
• Proficient written English communication skills.

Nice to have:

• Familiarity with jOOQ, JobRunr, Google Pub/Sub, Terraform, and MCP tools with Spring AI.

• Join the backend rotation and be part of on-call duties.
• Develop and maintain the Kotlin backend service integrating with payment, tax, manufacturing, and shipping partners.
• Participate in feature planning and selection together with product leadership and engineers.
• Build features end-to-end, including schema design through rollout and monitoring impact.
• Use coding agents and custom tooling for development tasks.
• Handle production incidents by switching off features, communicating with support, sizing impact, and fixing issues.
• Engage with support, growth, and fraud teams for cross-functional problem solving.

Remote work is limited to candidates located in Poland. Occasional meetings in Poznań are a plus but not required.