If you see the error "There was a problem creating your WebHook, please try again" while trying to add a Channels WebHook you need to make sure that the WebHook endpoint exists. As part of the validation process, the URL is checked in DNS to make sure that it exists.
For example if you add the WebHook URL http://mynonexistenturl.com this will fail because it isn't found by DNS.
You can check that your URL does return a result in DNS by using nslookup: