How to fix the error? header("Location:". $_SERVER['PHP_SELF']);?

Question

PHP

Warning: Cannot modify header information - headers already sent by (output started at C:\Server\domains\messbox\config.php:18) in C:\Server\domains\messbox\actions\login.php on line 12
on line 12 - header("Location:".$_SERVER['PHP_SELF']);
What could be the reason?

Answer 1

Headers can be sent BEFORE any output. That is, if you did echo, then the headers can no longer be sent, which PHP tells you about.
>Warning: Can't modify header information - headers already sent (output started in C:\Server\domains\messbox\config.php:18) in C:\Server\domains\messbox\actions\login.php on line 12