Forward Map not working

Hello,
I’m trying to configure dhcpd on linux to add forward maps to my zone.
After a lot of trial and error with my dhcpd.conf I got this configuration:

authoritative;

ddns-updates on;
ddns-update-style interim;
ddns-domainname “myzone.dynv6.net”;

deny client-updates;

update-static-leases on;

key “keyname”
{
algorithm hmac-sha256;
secret “SANITIZED SECRET”;
}

zone myzone.dynv6.net.
{
primary6 2a01:4f9:c010:95b::;
key “keyname”;
}

subnet6 XXXX:XXXX:XXXX:XXXX:XXXX:0001::0/96
{
range6 XXXX:XXXX:XXXX:XXXX:XXXX:0001:0000:0010 XXXX:XXXX:XXXX:XXXX:XXXX:0001:ffff:ffff;
option dhcp6.name-servers 2001:4860:4860::8888, 2001:4860:4860::8844;

group
{
host raspberrypi4
{
hardware ethernet xx:xx:xx:xx:xx:xx;
fixed-address6 XXXX:XXXX:XXXX:XXXX:XXXX:0001:0000:0002;
}
}
}

The problem is that updates request are rejected from the server with NOTIMP.
For example I get this log from my dhcpd:

Aug 01 18:10:53 giove.local dhcpd[77858]: Unable to add forward map from raspberrypi4.myzone.dynv6.net to XXXX:XXXX:XXXX:XXXX:XXXX:1:8602:ea0e: NOTIMP

Trying to sniff the traffic I found that the packet contains a prerequisite section that probably is not accepted by the server.

Do you know any workaround?

Regards,
Francesco