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 lef6bttp8lgcieubqhg1303ll1dbk9fe.builder.nu is not the root of its zone.
Instead, try zone transfer on builder.nu .
Instead, try zone transfer on builder.nu .