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 ns5016303.ip-15-235-84.net is not the root of its zone.
Instead, try zone transfer on ip-15-235-84.net .
Instead, try zone transfer on ip-15-235-84.net .