Delegated IPv6 to LAN Interface IP

[Ryushin]

I have delegated IPv6 working from my WAN to my LAN.  The WAN receives a /56 delegated range.  The LAN interface is configured to Track the WAN interface to get it's delegated IPv6 /64 range.  Everything seems mostly happy.  My only issue is that I can't seem to figure out a way to manually assign suffix IP of the LAN interface. For example, my prefix is 2605:1111:2222:a300 and my suffix IP is: ::aab8:e0ff:fe01:e172 so the IP address for the LAN interface would be: 2605:1111:2222:a300:aab8:e0ff:fe01:e172.  I want to manually assign the suffix so it will be something like this: 2605:1111:2222:a300::1.

I've been going down a rabbit hole for hours trying to solve this.  Any ideas on what I'm missing?

[dseven]

Set the "Optional Interface ID" (under "Track IPv6 Interface" in the Interface settings) to 1.

[Ryushin]

Set the "Optional Interface ID" (under "Track IPv6 Interface" in the Interface settings) to 1.

Perfect, thank you.