Accessing Mycodo using IPv6 fails


this may be a noob question, but I have an issue to access Mycodo using my Pi’s IPv6 address (typed in browser with brackets [ ). Is this even possible? The server is not reachable, connection refused. Using IPv4 from another PC in the network, works just fine.
I want to access Mycodo from outside my local network and my router doesn’t support IPv4 port forwarding. Thus I have to use the Pi’s IPv6 for access. Currently I cannot even access it from within the local network. Pinging IPv6 also works.
Any ideas? Thanks!