Parse invalid session token (Code: 209, Version: 1.7.1)

Check out this page: https://parse.com/tutorials/session-migration-tutorial

Most likely your app was using legacy session tokens. You can migrate to revocable session tokens by adding this to your app delegate right after you set the app id and client key.

    [PFUser enableRevocableSessionInBackground];

Parse's website has a section on handling this error that might be of more help to you: https://www.parse.com/docs/ios_guide#sessions-handleerror/iOS

Delete the app from the simulator or your phone, then rebuild and re-run the app. Sometimes an old token gets cached. I just solved this problem for my app.