2a01-168--0.hkfree.org IXFR zone transfer

Changes since SOA version

IXFR is a zone transfer request that returns changes since a specific SOA version. Enter the SOA version to request changes since then.

Not an apex domain The domain 2a01-168--0.hkfree.org is not the root of its zone.
Instead, try zone transfer on hkfree.org .