This, and the many other devices that use the Tuya platform, ie Smart Life, DO NOT work with the Google Assistant at this time. These devices will work with their apps, but not with Assistant. The issue is that even though linking this "app" and the assistant is successful the devices will not show up under "devices" to be controlled. There are a lot of recent post around the internet that report the same issues.
Also, this smart life app has its own assistant. You can ask the Google Assistant to "talk to smart life" and, sometimes, this will work. But the experience is less than satisfactory.