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 u18980100.wl101.sendgrid.net is not the root of its zone.
Instead, try zone transfer on wl101.sendgrid.net .
Instead, try zone transfer on wl101.sendgrid.net .