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 121-200-9-51.79c809.mel.nbn.aussiebb.net is not the root of its zone.
Instead, try zone transfer on 79c809.mel.nbn.aussiebb.net .
Instead, try zone transfer on 79c809.mel.nbn.aussiebb.net .