Urgent: Fix 500 Server Error in CodeIgniter App

I am in urgent need of a skilled PHP/CodeIgniter developer to troubleshoot and fix a critical issue in my web application. After operating smoothly for over three years, the platform has suddenly started showing a 500 Internal Server Error, and the cause is currently unknown.

Project Overview:

Application Framework: CodeIgniter
Issue: The application has abruptly begun to exhibit a 500 Internal Server Error.
Background: The platform has been functioning without issues for the past three years.
Current Status: The reason for the error is not clear, and I need expert help to diagnose and resolve it.
Key Requirements:

Strong experience in PHP and the CodeIgniter framework.
Proven track record in diagnosing and resolving 500 Internal Server Errors in web applications.
Ability to quickly identify and rectify the root cause of the error.
Excellent problem-solving skills and attention to detail.
Ability to communicate effectively and provide updates on the progress.
Scope of Work:

Conduct a thorough analysis to identify the cause of the 500 Internal Server Error.
Implement a fix to resolve the issue and restore normal functionality.
Ensure that the solution is robust and does not affect other functionalities of the application.
Provide a brief summary of the problem and the implemented solution for future reference.
Timeline:

Immediate start with a priority on quick resolution.