The Senior Backend Engineer will act as the primary technical owner of the Promotion Core Engine, a critical system responsible for promotion logic across both Transfer Wallet and Seamless Wallet architectures deployed in multiple regional markets. The engineer will be responsible for maintaining and enhancing the promotion logic to ensure reliable operation across all markets. This includes designing and maintaining promotion calculation algorithms, ensuring accurate promotion bonus computation, validating promotion reporting outputs, maintaining system integrity across multi-market deployments, and optimizing backend performance to support high transaction volumes. The focus of the role is on maintaining the core promotion engine logic while ensuring system reliability and scalability.