I have a service I am monitoring which makes a web service call. The web service call is being picked up by "Requests to unmonitored hosts" under Transactions & Services. I want to create a service for these calls. The following post shows how to do this for a certain IP address and port number but not for this specific case using either a domain or URL to define the service.
The post you referenced shows how to do this via a custom device which only lasts for 72 hours i.e. you will need to make this POST request to update the custom device every 72 hours. I have heard there are plans to add this feature to the product in the near future where once this is setup, it will remain permanent. For your use case to use a URL rather than IP, have you tried passing the URL into the configURL parameter to create the custom device to see if that works? Please see link on how to set this up and let me know if it works for you.