• Update your RouterOS
• Install or/and enable the IPv6 packages
• Configure the IPv6, disable IPv4
• Setup the firewall
• Setup the IPv6: 2803:1920:0:1::fff0/64
• Setup Neighbors, 2803:1920:0:1::1/64
• Settings, IPv6 Forward: Yes

Create:

• Name: TUNNEL, Prefix: 2803:1920:0:1::/64, Prefix Length: 64, here is the IPv6 range assigned for the Wan
• Name: PD, Prefix: 2803:1920:0:1::ff00:0/104, Prefix Length: 120, here is the IPv6 range assigned for the customer (Lan)

Create a server on interface where is linked to OLT lan (ethernet, normal fiber).