Finally, you will need to copy the base64-encoded SHA1 value to your Facebook app. You can do this by going to the “Settings” page in your Facebook app and adding the key hash to the “Key Hashes” field. Once you have added the key hash, your Facebook app will be able to communicate with the Facebook servers.

​https://stackoverflow.com/questions/23674131/android-facebook-integration-with-invalid-key-hash