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 ip.static.168-243-220-232.intercom.com.sv is not the root of its zone.
Instead, try zone transfer on intercom.com.sv .
Instead, try zone transfer on intercom.com.sv .