If you're still unable to login via your FB account. Maybe you | PGSharp Announcement Official

If you're still unable to login via your FB account. Maybe you can try the following workaround.

You have to do the step 1-2 through the original app.

Step 1. Link the game account to a Google Account. (If it's been linked, please ignore this step.)
Step 2. Unlink & link the Facebook account again in the app.
Step 3. Clear the data&cache of the default browser in your OS settings.
Step 4. Uninstall & install the PGSharp, then try again to sign in via the Facebook account in PGSharp.