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 ip4-spf.hkbn.com.hk is not the root of its zone.
Instead, try zone transfer on hkbn.com.hk .
Instead, try zone transfer on hkbn.com.hk .