Not an apex domain
The domain g.gandi-ns.eu.8.9.b.4.1.0.0.2.ip6.arpa is not the root of its zone.
Instead, try zone transfer on 8.9.b.4.1.0.0.2.ip6.arpa .
Instead, try zone transfer on 8.9.b.4.1.0.0.2.ip6.arpa .