OK @jezmck, if you remove your DNS1 and DNS2 entries and reboot your device, Pi-hole is going to start working. Right now it’s dependent on dnscrypt-proxy to start pihole; although the service says running, the internal services aren’t, which is why you can’t get to the web interface.
dnscrypt-proxy is failing to start because of this bug in the balena supervisor, but if you disable the DNS variables as mentioned above, Pi-hole will still work without it until the fix is deployed. You can also fully comment out the dnscrypt-proxy block within docker-compose.yml to just remove it for now.
Thanks for posting about the issue; I will update the guide/docs in whatever way we can so that other users aren’t caught by this.
Edit: as an alternative workaround, you can use balenaOS version v2.31.5 when adding your device to the application, which isn’t affected by the issue mentioned above and should work fine out of the box.