Worked on the Gozargah/Marzban repository to enhance the reliability and security of subscription-related API flows. Addressed a bug where incorrect HTTP status codes were returned for subscription errors by updating responses from 204 to 404, ensuring alignment with API contract expectations. Improved backend error handling by removing unnecessary exception details from responses, which reduced information leakage and made client-side debugging more straightforward. Utilized Python for backend and API development, focusing on robust error management and clear communication between server and client. The work contributed to a more predictable developer experience and helped prevent confusion for clients interacting with the subscription API.