Sync for iCloud, Sync for iCloud Contacts, and Sync for iCloud Mail do not support Apple’s latest authentication methods. Therefore, to log in to your account, you need to create an app specific password.
The steps below will show you how to check whether you have Apple’s latest authentication method enabled, and how to generate an app specific password. Each time you change your password, you must create a new app specific password.
1. Open your browser and go to icloud.com. Log in with your iCloud account.
2. Click on the ‘Settings’ icon.
3. Click on ‘Manage’ Apple ID.
4. Click on ‘Generate Password…’
5. Enter a name for the app-specific password and click ‘Create’.
6. Open Sync for iCloud/Sync for iCloud Calendar/Sync for iCloud Mail on your Android device and enter the password given by iCloud.