Need some help with player connections

When I tried to run my latest game for my players it gave us all a weird error saying it appears the connection appears to be closed. I have no idea what it is/means and the only thing I can find online is about setting up port forwarding. It didnt give me any issues prior to all this so I have no clue what to do. Has anyone gotten a similar issue and if so how did you fix it?

Are you able to provide a screenshot of this or is the error not appearing anymore?