How can the "Header already sent" error be fixed in PHP when uploading code to a live server?

The "Header already sent" error in PHP occurs when there is whitespace or output before the header() function is called. To fix this issue, make sure there is no output (such as echo, print, or whitespace) before calling the header() function. You can also use output buffering functions like ob_start() and ob_end_flush() to buffer the output and prevent headers from being sent prematurely.

<?php
ob_start(); // Start output buffering

// Your PHP code here

ob_end_flush(); // Flush the output buffer