How to read JSON file with PHP from instagram __a=1 page

I’m trying to call a URL and read its content using php.
when I place the url directly in the browser It works, but when I use php it returns me null.
here’s my code:

$url = "https://www.instagram.com/instagram/?__a=1"
$json = file_get_contents($url);
$res= json_decode($json);
var_dump($res);

Does anyone have an idea why I can’t read the file with PHP?
Thank you,