How do I request a IPv6 prefix on a dumb AP on a guest WiFi?

What is the correct way to request a IPv6 prefix for my TP-Link EAP615-Wall guest wifi. IPv4 subnet is working fine, I just need to add IPv6 to my guest wifi now. I am getting a /56 from my ISP for my WRT3200ACM router. Can a guest wifi from an access point request a /64 prefix from the main router?

"Usually", you'd define the the guest network on the main router (IPv4, IPv6, DHCP, DHCPv6, etc.). the APs usually just distribute the various networks you've defined, without providing any services to them (in particular no DHCP).

A multi-tiered approach is possible, but rarely the best option for a home environment with half a dozen APs in close proximity at most.

Looks like there is no way to request a IPv6 prefix from "guest" interface. Do I have to create a new LAN6 interface to request a IPv6 prefix?

The proposed setup is no longer a pure dumb AP, as it will locally route the guests. The trusted network could remain a dumb bridge.

Any routing requires two interfaces, one for the guests themselves and one facing upstream.

The upstream facing interface requests a prefix larger than /64 from the next router. The guests will use a /64 out of this prefix. Typically the guest-facing interface holds ::1 on this prefix so that DHCPv6 will work. The upstream facing interface does not necessarily need a GUA IPv6, but if it does it would be different from what the guests use. It almost always should have a GUA so that the router itself can initiate IPv6 connections to the public Internet, particularly DNS forwards.

Creating a new lan6 interface worked.

lan6 > Request IPv6-prefix of length = 64
lan6 > Advanced settings > IPv6 suffix = ::1

guest > IPv6 assignment length = 64