How to fix error in Header?

Question

PHP

Hello, I made an authorization system, but after the cookie is activated to redirect the user, it displays the following ...

Warning: Cannot modify header information - headers already sent by (output started at P:\home\test1.ru\subdomain\logins.php:5) in P:\home\test1.ru\subdomain\logins.php on line 12

Line 12 itself

if(isset($_SESSION["session_username"])){
header("location:glav.php");
}

I didn't find any spaces between <?php.
ANSI encoding (UTF-8 without BOOM did not help)
Line 5 and above
<?php require_once("includes/connection.php"); ?>

<?php
session_start();
?>
<?php require_once("includes/connection.php"); ?>
<?php include("includes/header.php"); ?>
<?php

Answer 1

I found an error, the problem was that the footer was sending the header, I deleted it and everything was fine.

Answer 2

This message indicates that you have already received a title from another location. And specifically, from the logins.php file, line 5. What do you have in it?
Check out the future . I think it will be useful. At the same time, you will understand what Rishat Kadyrov wrote to you about.

Answer 3

So it is written: the error occurred on line 12, and earlier information about the headers was sent on line 5 of the logins.php file. Look there.

Answer 4

This or another file has already sent headers.
Line 12 is not to blame for anything, look for the error above.