Setting up IPv6 on relay doesn't work

I have an ONT (Nokia G-240W-C). From it, I receive my ISP link. Up ahead, I have my main router. Previously, I used PPPoE authentication; however, there's a bug causing a slow connection. So, I decided to switch back to DHCP for a more stable and faster connection.

My router: DIR-878 A1

I receive 2 IPv6 addresses from my ISP: the first is /128, and the second is /64. I changed the protocol to use DHCP on my router, but when creating the DHCPv6 interface, I get both IPv6 addresses from the ISP, yet they don't associate with the "lan" interface. I tried using relay, but without success. Could someone help me?