Expert Backend and Database Fix for Existing Invoice System

We require an experienced freelancer to diagnose and resolve critical issues within our existing invoice system. The project involves comprehensive backend debugging, database repair, and ensuring all functionalities are restored and operating correctly. The goal is to stabilize the system and ensure reliable invoice processing. Specific tasks include: identifying root causes of current malfunctions, implementing necessary database fixes and optimizations, and performing thorough testing to validate the system's integrity and performance.