Over a two-month period, contributed backend development to the marcosdosea/gcm-ufs repository by building modular systems for payments, sales, and client management. Established foundational Java classes such as GerenciadorPagamentos and GerenciadorVendas to support transaction workflows, focusing on maintainable, object-oriented design. Migrated client data management from a legacy system, implementing CRUD operations and modernizing core classes to improve extensibility. Delivered end-to-end sales workflows, including finalization and cancellation features, while refactoring existing code to align with evolving business requirements. The work emphasized clean architecture and scalability, leveraging Java and backend engineering principles to position the project for future feature expansion.