The address we show here is the address Pi-hole uses when operating in Full IP blocking mode. Since we roll out unspecific IP blocking as standard mode, an empty IPv6 field is of no consequence at all for your Pi-hole.
As you're already quoting your setupVars.conf: The value of IPV6_ADDRESS will be shown in this field. If you want to see this field getting populated you can run pihole -r and select Reconfigure. This will also reconfigure your IP addresses. However, this should not be needed. Just use the 2403:.... address you found using ip a in your router*.
*) Check that this is in fact a static IP. There are many Internet service providers that change the IPv6 prefix on a regular basis. If you find that this is the case, you can go for an ULA based solution. See
Sorry to bother you, but i cant quite comprehend that part. What does my ISP have to do with this part? isnt the IPv6 address im using generated by the PI, and not my ISP?
IPv6 is very different from IPv4, it is basically an entirely new protocol. In contrast to IPv4, where only very few addresses are available, users started to establish their own local networks ("LANs"), all working within the very same address range (most often 192.168.0.0/16). The devices contacted the network through a NAT device, which is in almost all situations the router itself.
With IPv6, however, there are plenty of addresses available. Hence, it has been decided to remove the need for LANs and give a world-wide unique address to each of your devices. With IPv6, each device can reach each device directly over the Internet. With IPv4, devices can only reach NAT devices, involving additional hops that make the entire system slower and more power consuming.
As IPv6 addresses are unique on a world-wide basis, you can obviously not generate them yourself in your home network. Instead, you get a given prefix (most often the first half of the IPv6 address) assigned by your ISP. The second half of your IPv6 address can be managed locally by your devices. Another important distinction is that, for IPv4, you need either static IP address assignments or an DHCP server. With IPv6, your devices will self-negotiate their configuration. While you can install an DHCP server in an IPv6 network, this is strongly discouraged to do so because it defeats much of its powerful features.
I could go on for hours writing you about the differences, however, I strongly encourage you to read some tutorials or maybe wiki pages on the web for this.