Hi there,
Check if you are running the latest flyctl version (docs)?
See what LOG_LEVEL=debug flyctl m clone ... tells you?
Alternatively, if you are up for it, you can checkout, compile flyctl, and run the resulting binary, you should see failing commands echo out a full stack trace (prev). You could then report the issue back upstream.
The issue I faced was with regular machines which was subsequently fixed, and not with Fly Postgres v2.