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 a5cfqba2d850t0sa3lu0m7tsg0q4an49.builder.nu is not the root of its zone.
Instead, try zone transfer on builder.nu .
Instead, try zone transfer on builder.nu .