Google have recently made a change to how Smarter appliances are listed within Google Assistant, so you will need to re-link your device to get this to work. I have added some instructions below.
1. Go to Google assistant settings
2. Click on home control
3. Click on manage accounts at the top right of the screen
4. Press Smarter kettle and coffee and unlike your account
5. Search for Smarter and log in using Smarter account details
This will now have re-linked your account correctly and you can continue to use Google assistant to control your iKettle or Coffee machine.