URL redirection in php for Opera Mini browser

I would like to redirect all URLs opened from Opera Mini browser to specific browser using PHP. I have this code below but it is not working. Please help me.

if(! empty($_SERVER['HTTP_USER_AGENT'])){
    $useragent = $_SERVER['HTTP_USER_AGENT'];
    if(preg_match('@(Opera Mini)@', $useragent)){

        $host = $_SERVER['REQUEST_URI'];

        if($host !== 'mywebsite.com/browser-error'){
            header('Location: ./browser-error');
        }
    }
}