Sr Software Engineer - B/E

Rebuy Engine is on a mission to revolutionize shopping with intelligent, personalized experiences. As a Sr. Software Engineer, Back-End, you will own critical systems, particularly the billing and payments infrastructure, and contribute to a significant technical migration and platform enhancements.

Responsibilities:

• Design and build Rebuy’s centralized billing system that handles merchant billing, partner payments, and customer-facing charges
• Architect the integration layer that allows payment balances to be applied across Rebuy’s full suite of services
• Tackle genuinely complex financial engineering challenges with PHP and Go at scale
• Design and implement secure, well-structured APIs in PHP and Go to power billing events, payment processing, and financial data flows across our platform and Shopify integrations
• Lead and contribute to the migration of our Code Igniter 2 codebase to Code Igniter 4
• Partner with product and engineering to identify where AI agents can automate workflows, surface insights, and guide merchants through our product
• Build the backend systems — APIs, data pipelines, and event hooks — that enable intelligent automation
• Support a partner portal, data ETL pipelines, customer-facing reporting APIs, and the infrastructure that makes data flow reliably across the business
• Contribute significantly to the engineering culture at Rebuy by establishing, documenting, and promoting best practices
• Stay current with the latest security trends, vulnerabilities, and best practices as they apply to billing and payment systems
• Serve as a key technical anchor for PHP across the engineering organization
• Conduct quality checks on deliverables to ensure code, setup, and configurations meet expected results
• Engage actively in building a strong team culture
• Assist the Support team in triaging and resolving high-priority production issues

Requirements:

• Experience building or maintaining billing, payments, or financial systems — including working with payment processors, subscription engines, invoicing pipelines, or similar financial infrastructure in a production SaaS environment
• Educational background in CS // Engineering or a similar area
• 5+ years of hands-on experience building backend applications with PHP and Go, with a proven track record of delivering complex, high-traffic systems
• Experience designing and implementing secure, scalable, and maintainable RESTful APIs in PHP and Go, with a deep understanding of API design patterns, versioning, and performance optimization
• Experience with cloud-based technologies, preferably GCP
• Strong understanding of a performant SaaS environment
• Experience in a Scrum/Agile environment
• Experience with the Atlassian suite, including Jira and Bitbucket
• Solid understanding of security fundamentals as they apply to backend and financial systems — including secure coding practices, authentication/authorization patterns, data encryption, and awareness of current vulnerability trends (e.g. OWASP Top 10)
• A collaborative mindset and work approach with the ability to lead projects and mentor others
• The ability to thrive in a fast-paced environment with a high level of autonomy and responsibilities
• Excellent communication skills, especially being able to explain technical concepts to both technical and non-technical audiences
• Genuinely curious about the intersection of engineering and business
• You care about the downstream impact of what you build — not just that the code works, but that it moves the company forward