Can someone tell me why we can't use $_SERVER[REMOTE_ADDR] in php it's says some eror why plz tell me

Question

My code is here

https://code.sololearn.com/wmuiNVaK3LwA/?ref=app

Answer 1

Quoted from https://www.php.net/manual/en/reserved.variables.server.php

"$_SERVER is an array containing information such as headers, paths, and script locations. The entries in this array are created by the web server. There is no guarantee that every web server will provide any of these; servers may omit some, or provide others not listed here."