In March 2018 Facebook will invalidate calls from URIs not listed in the Valid OAuth redirect URIs requiring us to Enable Strict Mode for Redirect URIs.
If you tried all the solutions available googling about it without success you can try this fix too.
To fix this problem
a) Update and Enable Strict Mode and HTTPS in the app's settings.
b) Add in the app settings the valid OAuth redirect URIs the URL used to interact with Facebook SDK.
c) Change this piece of code:
$accessToken = $helper->getAccessToken();
In:
$accessToken = $helper->getAccessToken('myurl_callback');
} catch(Facebook\Exceptions\FacebookResponseException $e) {
...
}
That's all, this fixed the problem.