Adding any Invoice to Cart using REST API

Is it supported? If so, how do we accomplish it?

The case scenario is the following:

Allowing any (type of) users to find (all kind of) Invoice records (not necessarily their own) and add them to the RiSE Cart via REST API, thus enabling users to proceed with payments there.

This article gives some hints:
Posting an existing invoice to cart
But could not quite figure it all out yet.

Thank you for any assistance.