ddns update multiple zones in a single lan from dhcp server

I am trying to make the following setup to work but i'm failing :

A isc-dhcp server (debian) to update a bind9 server (debian).

The bind server has 2 zones: dev.toto and prod.toto, all servers (whatever their domains are, are in the same lan 10.5.0.0/16).

What I'm failing to achieve is to have the the dhcp server to add the correct entry to the correct zone.

Examples :

client1.dev.toto ask for a lease, the dhcp serves an ip and add an entry to the dev.toto zone file.

client1.prod.toto ask for a lease, the dhcp serves an ip and add an entry to the prod.toto zone file.

I tried to use :

option server.ddns-hostname = option fqdn.hostname;
option server.ddns-domainname = option fqdn.domainname;

To try and get / define the zone file automatically but it does not work as I expect, there is no more zone update.

/etc/dhcp/dhcpd.conf :

########### DNS UPDATE CONFIG
ddns-update-style standard;
allow client-updates;
update-conflict-detection false;
include "/root/dns.key";

option domain-name-servers 192.168.12.242;
option routers 10.5.255.241;

default-lease-time 1800;
max-lease-time 7200;

authoritative;

zone dev.toto. {
   primary 10.5.0.250;
   key rndc-key;
 }

zone prod.toto. {
   primary 10.5.0.250;
   key rndc-key;
 }

########### SUBNET DECLARATION
subnet 10.5.0.0 netmask 255.255.0.0 {
  range 10.5.1.1 10.5.1.254;
  option server.ddns-hostname = option fqdn.hostname;
  option server.ddns-domainname = option fqdn.domainname;
}

I can provide the named.conf.local if needed given that before trying to get this config working I did get the ddns update working so I guess there is nothing wrong with the bind9 side of the setup.

[EDIT 1]

I have the feeling that option 81 is what could fix my problem, or using some CLASS/SUBCLASS but: I cannot understand how to set up option 81, if anyone has an example I'd love that...