Not an apex domain
The domain 66-44-56-19.s6131.c3-0.grg-cbr1.lnh-grg.md.cable.rcncustomer.com is not the root of its zone.
Instead, try zone transfer on lnh-grg.md.cable.rcncustomer.com .
Instead, try zone transfer on lnh-grg.md.cable.rcncustomer.com .