As mentioned on our Facebook channels, we are aware of issues some users are having logging in via Facebook. We are in close contact with Facebook to try and resolve this issue as soon as possible. You should know that this issue has occurred entirely on their side, and as a result, they have suspended the game. Therefore it is largely reliant on Facebook solving it.
As soon as we have any updates, we will inform you. Please check #Known-Issues channel on our Discord for the most up-to-date information. We are sorry for any inconvenience caused.
Your Hero Zero Team