Over 6pn, one must connect to internal_port (8080?), not the (public) exposed one. But I see you did so, and it didn’t work.
If you do want to connect to public ports over 6pn, I think (not sure) you can do so over a Flycast address, which you must explicitly assign to an app.
For a Machine app, instead exec fly m status <vm-id> -d -a <machine-app-name> (docs).
If you haven’t already, then fly ssh console "[6pn-addr]" (ref) and exec netstat -alpn to see if things are listening on ports you expect them to.