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 cnmkv78h8iqs5huin8mn47bi8inmb7q6.heysender.dk is not the root of its zone.
Instead, try zone transfer on heysender.dk .
Instead, try zone transfer on heysender.dk .