When the ASA DHCP client sends a DDNS update, it needs to know its own hostname.
You can specify the hostname as hostname, as either a fully qualified domain name (FQDN) or as a hostname that is prepended to the ASA's domain name (configured with the domain-name command).
The client instructs the server to send only PTR updates, unless the server keyword is added, along with either the both (send both A and PTR updates) or none (send no DDNS updates) keyword.
This command can also be given as a global configuration command, to provide a global policy for all interfaces.
To resolve this issue, create a reverse lookup zone for the subnet that hosts the client computer in DNS.