Facebook PHP SDK 5 :: API 2.4 :: Cross-site request forgery validation failed. Required param "state" missing
I had to add this lines in some servers:
$helper = $fb->getRedirectLoginHelper();if (isset($_GET['state'])) { $helper->getPersistentDataHandler()->set('state', $_GET['state']);}I get this error randomly, depending of the server config.
session_start() at the beginning of both the scripts. I got solution from here: https://github.com/facebook/facebook-php-sdk-v4/issues/473
If you're using a "www" version of your site to generate the login link and you get redirected to the non-www version, you'll run into issues with your session. So make sure you access the www version of your site and then define the callback url to the same www version. Also, you can define permanent redirects in your server configuration to make sure anyone accessing your site from the non-www version gets redirected to the www version or vice versa.