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 50-170-231-185.ripe.as60456.net is not the root of its zone.
Instead, try zone transfer on ripe.as60456.net .
Instead, try zone transfer on ripe.as60456.net .