Worked on the CAUSW_backend repository to enhance data integrity and API reliability by addressing a critical validation issue during user sign-up. Focused on backend development using Java, the work involved implementing a validation mechanism to ensure that the first four digits of the student ID matched the admission year, thereby preventing invalid sign-up requests at the API layer. Exception handling was improved by introducing explicit error messages for invalid user data, which provided clearer feedback and reduced ambiguity for users. These changes strengthened backend validation, improved onboarding quality, and minimized downstream data issues, aligning with reliability and data quality objectives.