Explicitly sharing files externally

Requirement: Let user A (in tenant/org Y) share a file with user B (in tenant/org Z) and allow user B to access or copy this file to their storage programmatically.

Can this be achieved? I have tried the following -
"/copy" endpoint with either user's authentication results in 404 error - The resource could not be found.

"/invite" endpoint with user A's authentication, then "/sharedWithMe?allowexternal=true" with user B's authentication - does not list the shared file.