Worked on the getlago/lago-go-client repository, focusing on backend development and API design using Go. Delivered two core features over two months, starting with a configurable subscription invoice issuing date system that enhanced billing flexibility and data integrity by introducing enums for anchor dates and adjustment methods, as well as enforcing mandatory fields for customer billing configurations. Later, implemented an offset option for OnTerminationCreditNote, enabling more flexible handling of termination credits and reducing manual adjustments. The work emphasized maintainable code, clear commit messaging, and type augmentation, resulting in improved API safety and alignment with evolving business billing requirements.