I'm setting up an WireGuard tunnel between my VPS and my home network. This
tunnel should be IPv6 only.
I assigned the IPv6 subnet fd00:1:a/64 to my home network and my wireguard
client got the static IP fd00:1:a::1.
On the VPS I assigned the IP fd00::1 to the wg0 interface.

Here're the configs:
*Client:*


[Interface]
PrivateKey = XXXX
Address = fd00:1:a::1/64
[Peer]
PublicKey = XXXX
AllowedIPs = fd00:0:0::/64
EndPoint = vpn.domain.tld:51820
PersistentKeepalive = 25

Server:


[Interface]
PrivateKey = ...
ListenPort = 51820
Address = fd00:0:0::1

[Peer]
PublicKey = XXXX
AllowedIPs = fd00:1:a::/64
It *might* work if at the client side you use
Address = fd00:1:a::1
instead of
Address = fd00:1:a::1/64
However, the safest way to make it work is for the [Interface] Address at each end to be a separate point-to-point subnet.  These are the addresses allocated to the wg0 interface itself.  I don't know if "unnumbered" point-to-point links are supported by Wireguard (that is, when you re-use an address from a subnet that belongs to a different interface), but I know it definitely works with a separate link subnet.

So if you want to use the whole block fd00:0:0::/64 in your VPS, then I suggest you allocate a new subnet for the point-to-point, e.g.

client

[Interface]
Address = fd00:2::2/64

server

[Interface]
Address = fd00:2::1/64

AllowedIPs are then still the remote subnets at each side, as you have now.

If your VPS is just a single host with a single IPv6 address on the wg0 interface, then you can keep it as you have now but use

server

[Interface]
Address = fd00:0:0::1/64

client

[Interface]
Address = fd00:0:0::2/64

HTH,

Brian.