185-50-21-103.fttx.thn.uk.ctw.net 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 185-50-21-103.fttx.thn.uk.ctw.net is not the root of its zone.
Instead, try zone transfer on ctw.net .