How to fix CodeIgniter URL issue?

I moved my CodeIgniter app from a subdomain to a subdirectory under my main domain. However, accessing pages under the subdirectory removes the subdirectory from the URL, resulting in a not found page. I have updated the base URL in the config file, but the error persists. How can I fix this issue without changing every link in the application to include the subdirectory in the URL? Below is my .htaccess file.