When signing in with Facebook, you might have not provided us with your e-mail address. Please verify this by tapping the "Review the info that you provide" link during the sign in process, as illustrated below:
If the toggle for your email address is switched off as shown here...
...the app will not be able to find your account and you will see the following error message:
The solution is to make sure that the toggle is switched ON, and try again.
If this didn't help, please contact our customer service and we will help you to resolve this.