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 app-a-de.c-549.maxcluster.net is not the root of its zone.
Instead, try zone transfer on c-549.maxcluster.net .
Instead, try zone transfer on c-549.maxcluster.net .