ua-19.metrooptic.com.163.21.50.in-addr.arpa 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 ua-19.metrooptic.com.163.21.50.in-addr.arpa is not the root of its zone.
Instead, try zone transfer on 50.in-addr.arpa .