I have followed the guides for copying users from a source zcs 6.0.5 server, and have successfully recreated the domains and users of those domains on a new server, running zcs 6.0.8. I can log in to the new server using the passwords from the old server, so all seems well there.
Next I create archives of the accounts on the old server with:

/opt/zimbra/bin/zmmailbox -z -m USER@FQDN.NET getRestURL "//?fmt=tgz" > USER@FQDN.NET.tgz

Which yields what appear to be valid archives.
Unfortunately when I try to restore those archives on the new server with:

/opt/zimbra/bin/zmmailbox -z -m USER@FQDN.NET postRestURL '//?fmt=tgz&resolve=reset' USER@FQDN.NET.tgz


curl -k -u DOMAINADMIN:ADMINPASS --data-binary @/USER@FQDN.NET.tgz "https://FQDN.NET:7071/service/home/USER@FQDN.NET/?fmt=tgz&resolve=skip

I receive an error:
ERROR: service.FAILURE (system failure: POST failed, status=401 must authenticate)

I have tried running these restore commands as root and as the zimbra user, with the same results. What might I be doing wrong?