What is the URL / endpoint for calling an Object Function?

Summary:

I cannot find all the necessary information necessary for calling an "Object Function" written in Groovy via a REST API from an external REST client.

Content (required):

The following article describes a POST request's content-type and body used to invoke the object function.

https://support.oracle.com/cloud/faces/DocumentDisplay?id=2361316

Unfortunately, the article doesn't tell me what URL to use for the POST request. There is a link to the documentation, but the link only brings me to the top-level documentation, not the information I need.