Not an apex domain
The domain 2001-1960-010f-0002-0000-000f-0007-0002.ff219bca05b4e7cc58d1c65996f8e2bc.ip6.frontiernet.net is not the root of its zone.
Instead, try zone transfer on ip6.frontiernet.net .
Instead, try zone transfer on ip6.frontiernet.net .