Worked on the Studio73/l10n-spain repository to address critical gaps in Spanish tax reporting data for improved localization and regulatory compliance. Focused on backend development and data configuration, the work involved correcting AEAT Modulo 303 mappings and enhancing SII data coverage to ensure all required tax fields are accurately emitted. Using Python and CSV, the developer mapped intra-community acquisitions and imports to the appropriate reporting lines, reducing the risk of missing entries and compliance issues. The changes, delivered through targeted bug fixes, strengthened the reliability of tax reporting workflows and ensured that localization data met Spanish regulatory standards.