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 reverse-proxy-01.testing.unlp.edu.ar is not the root of its zone.
Instead, try zone transfer on testing.unlp.edu.ar .
Instead, try zone transfer on testing.unlp.edu.ar .