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 correo.hospital.uncu.edu.ar.135.12.200.in-addr.arpa is not the root of its zone.
Instead, try zone transfer on 135.12.200.in-addr.arpa .
Instead, try zone transfer on 135.12.200.in-addr.arpa .