A Coupa software developer is responsible for building, testing, and maintaining software systems within the Coupa platform, a cloud-based spend management system. They utilize programming languages like Ruby, Java, and Python to develop applications. They collaborate with other developers, UI designers, and business analysts to create user-friendly solutions that improve procurement, expense management, and invoice processing. They also debug issues, optimize code, and ensure the software adheres to quality standards. Their role involves understanding business requirements, implementing new features, and enhancing the existing functionalities to improve the overall user experience within the Coupa software.