https://forum.blockland.us/index.php?topic=312688.0This topic on the same page has the same issue.
There are 2 things:
-- UPnP is not always reliable
-- The master for UPnP could be down
You have 2 options:
-- PM Badspot and tell him to restart the matchmaker
-- Learn how to port forward (there are many sources of how to port forward, simple google searches, search on forums for a
tutorial)
A great thing about port forwarding is that once you do it, you never have to do it again until your local IP changes/new router/different port or something is using the port you forwarded; 90% of the time you get a ping which anyone is able to join.