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 x5ab9012a.customers.hiper-net.dk is not the root of its zone.
Instead, try zone transfer on customers.hiper-net.dk .
Instead, try zone transfer on customers.hiper-net.dk .