HarmonyNetwork

The client seems to connect you to a singleplayer world instead of the server, maybe try updating to the latest version of ClassiCube and connecting again.

I recommend using another file hosting service for the time being, such as catbox.moe to tumblr. Turns out, the error is because ClassiCube parses the ampersand (&) as percent (%) instead of what it should be.

Loads fine in browser, it's the server that has the issue.

What I get from trying to use /img is a 403 error, which means the server cannot access the file. Unfortunately, this seems to be a Dropbox issue, I recommend using something like https://catbox.moe/ instead.

In more recent versions of MCGalaxy, you can use links from dropbox and the like as long as it is less than 128 characters and has the file extension in it. As for the MCGalaxy.exe file, that would be on the computer of whoever's hosting the server.

MCGalaxy 1.9.5.0 is already out, so you'll probably have to wait until the next version update in a few years.

There are other server softwares, however, MCGalaxy is the most used one, and is typically up to date with the client, as they are made by the same developer.

The built-in browser is called Silk. I've tried using this to play CC, and it crashes because of some features not being present that CC uses.