First things first: you need to check with your ISP that they are fully dual stack, and the block that's being allocated to your WAN interface is properly routed etc.. It's also a good opportunity to ask them whether it's dynamic or static, and whether /64 is the only block size they'll allocate [1].Assuming the range is genuine and available for your use, the starting point is to make it available on your LAN interface. Edit your LAN interface and under 'IPv6' select 'track interface' and select the WAN interface you're getting the v6 range from.