This is controlled by the parameter allow-axfr-ips in the PowerDNS configuration file (/etc/powerdns/pdns.conf) inside the PBA-S server. PowerDNS has to be restarted after the configuration file is modified:
# service pdns restart
Only these IP addresses or netmasks will be able to perform
AXFR transfers. Thus be sure you setup all IP addresses of your nameservers.
allow-axfr-ips=192.168.101.100/0 192.168.5.103 192.168.102.112
It is recommended to allow AXFR requests only for PBA-S managed DNS servers.