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