[php] header('HTTP/1.0 404 Not Found'); not doing anything

I have a 404.php file in my site's main directory and I was using header('Location: 404.php'); for a while until someone said that you should use header('HTTP/1.0 404 Not Found'); instead. So I replaced it with that and then added: ErrorDocument 404 /404.php to my apache config file and restarted the server but it doesn't work.

I tried different variations including ErrorDocument 404 404.php and ErrorDocument 404 mywebite/404.php but to no avail.

What I mean by doesn't work is that earlier when using header('Location: 404.php'); it would redirect to the 404.php file but when I replace it with header('HTTP/1.0 404 Not Found'); it seems to just skip over the line and not do anything. It most certainly is not redirecting. The reason I am calling for the redirect is because if a $_GET header value is not recognized the page should 404.

After writing

header('HTTP/1.0 404 Not Found');

add one more header for any inexisting page on your site. It works, for sure.

header("Location: http://yoursite/nowhere");
die;

You could try specifying an HTTP response code using an optional parameter:

header('HTTP/1.0 404 Not Found', true, 404);

Another reason may be if you add any html tag before this redirect. Look carefully, you may left DOCTYPE or any html comment before this line.

For PHP >= 5.4 you can use a simpler function like this : http_response_code(404);
PHP Documentation

i think this will help you

content of .htaccess

ErrorDocument 404 /error.php
ErrorDocument 400 /error.php
ErrorDocument 401 /error.php
ErrorDocument 403 /error.php
ErrorDocument 405 /error.php
ErrorDocument 406 /error.php
ErrorDocument 409 /error.php
ErrorDocument 413 /error.php
ErrorDocument 414 /error.php
ErrorDocument 500 /error.php
ErrorDocument 501 /error.php

error.php and .htaccess should be put in the same directory [in this case]

Use these codes for 404 not found.

if(strstr($_SERVER['REQUEST_URI'],'index.php')){
  header('HTTP/1.0 404 Not Found');
  readfile('404missing.html');
  exit();
}

Here 404missing.html is your Not found design page. (it can be .html or .php)