What Slack URL To Use When Creating an Alert Policy via API?

When using the DigitalOcean API (or terraform) to create an Alert Policy for droplets with a Slack Notification, you need to provide the Slack Hook URL. I tried the following:

(1) Creating an own custom Slack App with a webhook, then use that webhook URL (=> does not work, although there is no error message during alert policy creation)

(2) Looking through DigitalOcean and Slack UIs to find the URL of an already existing and working webhook from the Digitalocean Slack app so I can use it (=> did not find it)

(3) Using the Digitalocean API to list alert policies and then getting the URL of an already existing and working webhook (=> works)

Did I miss anything conceptually or in the UI or the docs? Is there a better way that’s more “usable”? FYI, the end goal is full terraform automation of alert policy management.