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 ns323664.ip-37-187-156.eu is not the root of its zone.
Instead, try zone transfer on ip-37-187-156.eu .
Instead, try zone transfer on ip-37-187-156.eu .