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 a4ba-3bff-fe08-31e1.v6.us-nyc1.upcloud.host is not the root of its zone.
Instead, try zone transfer on v6.us-nyc1.upcloud.host .
Instead, try zone transfer on v6.us-nyc1.upcloud.host .