If you previously were able to play Arcane Legends using Facebook login but are no longer able to after updating the client, here is what you can do to correct the issue:
Go into Settings
Scroll down to Facebook
You should see a list that says "Allow these apps to use your account:"
Please set Arcane Legends to ON
If you need further assistance, please contact Spacetime Studios Support via our Support Website at http://support.spacetimestudios.com or by writing email to email@example.com