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 _7df9abd39f633e76f49f6d687dff3203.pbtest.appletree.co.uk is not the root of its zone.
Instead, try zone transfer on bpxxncpwjz.acm-validations.aws .
Instead, try zone transfer on bpxxncpwjz.acm-validations.aws .