Hi guys Where can I find the webhook

[daring cobalt]

I answered this myself.

The documentation is a bit poor regarding this. Mainly, you need to add the webhook url to the list of callback urls in your Withings developer application setup.

In order to see the url that Home Assistant has generated, you need to turn on the logger and enable debug for the Withings component. Then you can see the url in the logs.

If you have any sort of reverse proxy, like Authelia, you need to add either a regex for all your webhooks or allow the specific webhook url through.

Home Assistant must be able to successfully register this webhook url in order for you to be able to successfully test the url from your Withings developer application screen.

Once all the above is done, the "in_bed" sensor will go from unavailable to detected or clear after the sensor state has changed at least once.