Don’t bother. Their IPv6 setup is notoriously broken. They have a number of IPv6 misconfiguration in their core switches which makes using IPv6 with your own hardware almost impossible.
Unfortunately it seems they’ve also let go of all their good network admin. It used to be possible to find someone at Hyperoptic capable of investigating and fixing these issues, but no more.
Something definitely changed around COVID time, they stopped providing the info to set up your own kit freely, they wouldn't put you in touch with L3+ tech anymore and you couldn't connect your own kit without cloning IDs.
I had an issue one time, around 2020 and I couldn't fit the life of me get past a zero-knowledge L1.
Back in 2017-18 when I joined they put me in touch with one of their network engineers who helped me configure my EdgeRouter.
I've been using their IPv6 for years on my Turris Omnia (TurrisOS is based on OpenWRT and also open source) plugged directly to their switch. Everything works via DHCPv6 and RA. I get a /56 PD that I can use for my LAN subnets as I wish. The IPv6 Internet is fast and stable.
I also used their IPv6 setup for years. But then it got broken after they did maintenance, and I’ve never been able to get it fixed.
I’ve talked to insiders about this stuff, and there’s a number of known long running misconfigurations issues. Which unfortunately I’ve probably been hit with. I’ve also been told the odds of it getting fix via support is zero at this point.
In my case their switches refuse to assign an IP to any of my gear. My config hasn’t changed, and I’ve done some pretty in depth debugging. TL;DR I need to spoof some non-compliant with my gear to get their gear to play ball. I’ve zero interest in playing that game, I need IPv6 to be rock solid reliable, or it’s just not worth the effort.
Unfortunately it seems they’ve also let go of all their good network admin. It used to be possible to find someone at Hyperoptic capable of investigating and fixing these issues, but no more.