During November 2024, Alex Pardo focused on backend development for the invopop/gobl repository, delivering the Verifactu addon to enhance Spain-specific tax compliance. He implemented automated extensions and validation rules for invoices, addressing exemption and correction-type keys, and ensuring comprehensive validation for invoice customers, preceding documents, lines, and taxes. Working in Go, Alex designed the addon to integrate seamlessly with the GOBL system, supporting internationalization and laying the foundation for scalable, country-specific compliance modules. The work demonstrated depth in regulatory logic and extensibility, with the addon registered and production-ready, providing a robust framework for future compliance-driven feature development.