If you typically use Facebook to login to Pokémon Go, you may have encountered an error when you trying to do so recently. Players have been reporting issues with logging in via Facebook, noting that a message pops up listing the feature as unavailable.
The error message specifically says “Feature Unavailable: Facebook Login is currently unavailable for this app” when players try to login. This has the same effect as other “failed to log in” or “unable to authenticate” pop-ups, and Niantic has some general fixes for players to try.
First, it is recommended that you try to close out of the app and attempt to login again, while also checking that you have a stable network connection. This could fix the issue by simply resetting any errors or loading in any updates.
Additionally, you should make sure that your Pokémon Go app has been updated to the most recent version to make sure there aren’t bugs or fixes that have been applied.
If neither of those options fix your problem, it could very well be an issue affecting Niantic’s servers. In that case, you will likely need to use another method to sign into the game or wait a little bit before trying again.