Abhinav Gupta enhanced the juspay/decision-engine repository by developing mandate and e-mandate processing features that improved the accuracy of gateway selection for diverse payment scenarios. He implemented logic in Rust to correctly identify and process one-time mandate flows, broadening transaction coverage and ensuring compliance across gateways. Abhinav also addressed a syntax error and refined authentication type validation within the gateway filtering logic, which reduced edge-case failures and improved routing robustness. His work demonstrated strong backend development and API integration skills, with careful attention to data-flow and testing, resulting in smoother mandate processing and more reliable payment gateway operations for the platform.