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 20.d2.c1ad.ip4.static.sl-reverse.com is not the root of its zone.
Instead, try zone transfer on ip4.static.sl-reverse.com .
Instead, try zone transfer on ip4.static.sl-reverse.com .