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 static-71-246-237-73.washdc.fios.verizon.net is not the root of its zone.
Instead, try zone transfer on washdc.fios.verizon.net .
Instead, try zone transfer on washdc.fios.verizon.net .