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 _acme-challenge.sakyant.isl.net.tw.sakyant.isl.net.tw is not the root of its zone.
Instead, try zone transfer on isl.net.tw .
Instead, try zone transfer on isl.net.tw .