Facebook API Error Code: 191 - facebook

Question

I would really appreciate some help. I've searched around, and I feel like I've tried everything but to no avail.
API Error Code: 191
API Error Description: The specified URL is not owned by the application
Error Message: Invalid redirect_uri: Given URL is not allowed by the Application configuration.
These are my settings:
App Domains: localhost
Canvas URL: http://localhost/friendsmash/
Secure Canvas URL: *empty*
App Available to Public: No
Valid OAuth redirect URIs: http://localhost/friendsmash/
Edit:
I get the error when I try to go to the canvas URL. In other words, I put:
http://localhost/friendsmash/
in my browser. It redirects me here: https://www.facebook.com/dialog/oauth?client_id=592670390826338&redirect_uri=https%3A%2F%2Fapps.facebook.com%2Ftestappertest%2F&state=8712a908d02c6b6fc3fa9c19c9747296&scope=email%2Cpublish_actions
Then, I see the error. When I go to the canvas page instead, I get a blank page. As for the code, I am following this tutorial: https://developers.facebook.com/docs/games/canvas/canvas-tutorial
I censored the app id and secret. Anyway, this is the relevant part of the code:
<?php
require 'server/fb-php-sdk/facebook.php';
$app_id = 'XXXXXX';
$app_secret = 'XXXXXX';
$app_namespace = 'testappertest';
$app_url = 'https://apps.facebook.com/' . $app_namespace . '/';
$scope = 'email,publish_actions';
// Init the Facebook SDK
$facebook = new Facebook(array(
'appId' => $app_id,
'secret' => $app_secret,
));
// Get the current user
$user = $facebook->getUser();
// If the user has not installed the app, redirect them to the Login Dialog
if (!$user) {
$loginUrl = $facebook->getLoginUrl(array(
'scope' => $scope,
'redirect_uri' => $app_url,
));
print('<script> top.location.href=\'' . $loginUrl . '\'</script>');
}
?>