How do I configure a virtual server in nginx to listen only on IPv6

For my website I need effectively 3 domains:

• example.domain: accessible via both IPv4 & IPv6
• ipv4.example.domain: accessible via IPv4 only
• ipv6.example.domain: accessible via IPv6 only

I tried to solve this using the following nginx config:

server {
    listen [::]:80 ipv6only=off default_server;
    listen 80 default_server;
    server_name example.domain;
}

# IPv4 only endpoint
server {
    listen 80;
    server_name ipv4.example.domain;
}

# IPv6 only endpoint
server {
    listen [::]:80 ipv6only=on;
    server_name ipv6.example.domain;
}

But this throws the error: nginx: [emerg] duplicate listen options for [::]:80 for the IPv6 server block (line 15 in my example).

How can I achieve the desired result? Would I be required to use 2 separate IPv6 addresses to host these websites on?

You are misunderstanding the ipv6Only listen flag, if it is set to off, you get a dual-stack socket, while if it is set to on it makes an IPv6 socket

You need the following config:

server {
    # listen on IPv6 only
    listen [::]:80 ipv6only=on default_server;
    # listen on IPv4 only
    listen 80 default_server;
    server_name example.domain;
}

# IPv4 only endpoint
server {
    # listen on IPv4 only
    listen 80;
    server_name ipv4.example.domain;
}

# IPv6 only endpoint
server {
    # listen on IPv6 only
    listen [::]:80;
    server_name ipv6.example.domain;
}

If a request comes in on the [::]:80 server socket, NGINX knows it has to match to the servers ipv6.example.domain or example.domain, falling back to example.domain if there is no match.