Getting undefined: Request could not be proxied!

workspace
php

#1

Only one particular header call cannot be proxied, not sure why.

specifically when trying to redirect form this php script

    <?php
    session_start();
    if(!isset($_SESSION['user'])){
    $_SESSION['warning'] = '<div class = "callout alert" data-closable><h5>Error</h5><p>You cannot try to add   favourites unless you are logged in</p> <button class="close-button" aria-label="Dismiss alert" type="button" data-close><span aria-hidden="true">&times;</span></button></div>'; 
    header('location : index.php');
            
        }

    if(!isset($_SESSION['userFav'])){
        $_SESSION['userFav'] = array($_GET['id']);
        
    }
    else{
        array_push($_SESSION['userFav'], $_GET['id']);
    }
    $_SESSION['success'] = '<div class = "callout success" data-closable><h5>Success!</h5><p>Favourite has been added</p> <button class="close-button" aria-label="Dismiss alert" type="button" data-close><span aria-hidden="true">&times;</span></button></div>';
    header('location : favs.php ');
    ?>