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 pr51-mxa-nlb-3b0a86b0084c3e1b.elb.us-west-2.amazonaws.com is not the root of its zone.
Instead, try zone transfer on elb.us-west-2.amazonaws.com .
Instead, try zone transfer on elb.us-west-2.amazonaws.com .