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 94-237-26-240.de-fra1.upcloud.host is not the root of its zone.
Instead, try zone transfer on de-fra1.upcloud.host .
Instead, try zone transfer on de-fra1.upcloud.host .