Thanks for guiding me. Actually I was not aware of case-sensitivity in Linux and this issue was due to it. Windows is not case-sensitive but Linux is. When I changed my folder name is app/Httpd/Controller/API and also in php.ini, I issue got resolved in my Ubuntu machine. But When I deployed it on Portainer I got the the older image content. So I run "sudo docker system prune -a", all the caching and unused images are removed and my application started working fine. I really appreciate you guys helping me to sort this issue. Thank you very much.