Backend Engineer (Platform)

Sunollo is building a premium residential energy platform that combines high-quality hardware, reliable installation operations, and software to make clean energy simple for homes in Singapore. We are looking for a Backend Engineer (Platform) to design, build, and own revenue-critical backend systems. The initial focus of this role is to build the foundation of our billing platform, followed by broader platform and internal systems. This role is suitable for a senior backend engineer who enjoys high ownership, clear scope, and building production systems that are reliable and maintainable. Key Responsibilities Design and implement backend systems that are revenue-critical and operationally important Build a billing and invoicing engine supporting subscriptions and milestone-based payments Design clean, auditable data models and event logs with replay safety Integrate with third-party systems such as Xero using OAuth2, APIs, and webhooks Implement secure and reliable background jobs and workflows (subscriptions, reminders, billing milestones) Ensure system reliability through logging, monitoring, alerting, and failure recovery mechanisms Build backend APIs to support internal admin tools and customer-facing applications Collaborate closely with product, finance, and operations teams to deliver correct system behaviour Write well-tested, maintainable code for critical system paths Job Requirements Must Have Strong backend engineering fundamentals with experience shipping production systems Experience with PostgreSQL and practical database design Experience building and operating API integrations (OAuth2, webhooks, retries, idempotency) Strong understanding of system reliability, monitoring, and failure handling Ability to work independently with high ownership and minimal supervision Good to Have Experience with billing systems, subscriptions, invoicing, or payments Experience integrating accounting or CRM systems (e.g. Xero, HubSpot, Salesforce) Experience with Supabase or managed Postgres / serverless environments Experience building internal tools or admin dashboards Startup or fast-growth company experience Qualifications Degree in Computer Science, Engineering, or related field (or equivalent practical experience) Senior level preferred (5+ years of backend engineering experience); strong mid-level candidates may be considered