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 115.ip-51-38-238.eu is not the root of its zone.
Instead, try zone transfer on ip-51-38-238.eu .
Instead, try zone transfer on ip-51-38-238.eu .