2001-1960-0020-6000-0000-0000-0000-0000.f45216b0bf237b38bf82ce18ffcc9927.ip6.frontiernet.net AXFR zone transfer

Not an apex domain The domain 2001-1960-0020-6000-0000-0000-0000-0000.f45216b0bf237b38bf82ce18ffcc9927.ip6.frontiernet.net is not the root of its zone.
Instead, try zone transfer on ip6.frontiernet.net .