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 2018953.spf06.hubspotemail.net is not the root of its zone.
Instead, try zone transfer on spf06.hubspotemail.net .
Instead, try zone transfer on spf06.hubspotemail.net .