Google Play Services are not compatible with Amazon Kindle Devices and is therefore not possible to sign in with a Google+ account. Attempting to do so will result in the following error message "Oops! We couldn't Authenticate you."
The workaround if using an Amazon Kindle Device is to attempt to login with your Facebook Account instead as this should work. Note that Google+ sign ins should still work with most Android devices on the market and this only applies to Amazon Kindle devices.
If you are getting the above error but not using an Amazon Kindle device, please send a support email through to us as this will be unrelated!