My webapp has a login/logout function, In safari of iphone I can't logout, it seems like my php script can't cancle cookie

I create a login/logout function for my web project with php, It works fine with browser in pc and browser in Android. But in iphone it dosen't work, some time I can not logout, it seems like my php script can't cancle cookie. I use this code for login by setting cookie: session_start(); setcookie("us", $email, time() + (86400 * 30), "/", $_SERVER['SERVER_NAME'], isset($_SERVER["HTTPS"]), true); setcookie("ps",$password, time() + (86400 * 30), "/", $_SERVER['SERVER_NAME'], isset($_SERVER["HTTPS"]), true); I use this for logout by cancle cookie: session_start(); setcookie("us", null, time()-3600, "/", $_SERVER['SERVER_NAME'], isset($_SERVER["HTTPS"]), true); setcookie("ps", null, time()-3600, "/", $_SERVER['SERVER_NAME'], isset($_SERVER["HTTPS"]), true); setcookie("PHPSESSID", null, time()-3600, "/"); $_SESSION = array(); session_unset(); session_destroy(); header('Location: [login to view URL]'); When start my page the php will check if there is cookie for login automatic: session_start(); if(isset($_COOKIE["us"])){ //verify this user... }