IPv6 networks require an IPv6 router to distribute Router Discovery (RD) advertisements.
RD advertisements allow clients to be aware of prefix information and behavior flags in the IPv6 network. In DHCPv4, the default router information is returned by DHCP server as an option, as opposed to DHCPv6, where this role is vested in real routers with IPv6 support. There are other systems that can perform RD advertisements, such as Debian Linux. If you don't have an IPv6 router in the IPv6 network, you can still use alternative solutions to implement the role of RD advertiser.
By default, certain clients won't support IPv6. Without proper IPv6 support enabled, you won't be able to route packets from your client system to either Address Manager or DNS/DHCP Server for IPv6 communication. Refer to your client vendor’s manual to learn more about how to configure your system to be used as an RD advertise or how to enable DHCPv6 for your client.