The curtain integration provided by the user above works by communicating with HA via BT and not the Switchbot Hub. Since your HA is install 3 floors down, it is out of range. Does your NAS have BT?
As far as I know, there is no HA Integration to talk to the hub. However, there is a switchbot api method you can try which needs the hub to communicate. Request a token via the mobile app feedback. I don’t have a hub to test. But an example of a way to trigger via HA is by curl.
curl "https://api.switch-bot.com/v1.0/devices" -H "authorization: YOUR_TOKEN_KEY"
The downfall to the api method is that, if you lose internet connection, you will not be able to trigger your devices. An alternative is to move your HA closer to the curtain device or install another server (ex. rpi) and try my method.
There is another method I have found recently that uses ESP32 to connect to the device. It is setup for 2 bot devices and the author claims it should work for the curtain devices as well, but not tested.