What I did to fix this was alter the code slightly:
um-social-login-facebook.php
Line: 86
Found that if I entered the URL to my login page it all worked hunky dory…
Change: $accessToken = $helper->getAccessToken();
To: $accessToken = $helper->getAccessToken(“https://www.EXAMPLE.com/login/?provider=facebook”);
Naturally, when this plugin updates it will kill my temp fix.
FYI – my site runs fully over https:// – I think this might be the reason but not 100% on that.
