Hi there,
I have installed the latest EchoPet JAR file, but it isn't working with my server. My server is running Spigot, but I am unsure of the exact build. All I know is that the Spigot build I am running supports Minecraft version 1.7.* and 1.8, which the latest version of the plugin JAR is meant to handle. Whenever trying the /pet command, it says that it is an unknown command, and as far as I know, it isn't even showing when doing the /pl command on the server.

Copy+pasting from the last two recent tickets that have been opened about this (e.g. #437, #439, #421, #418, etc.):

There is an announcement on the BukkitDev page which explains exactly why this is happening:

If EchoPet is not loading on your Spigot 1.8 build and your server is outputting "Skipping loading of EchoPet as it does not work with Spigot 1.8 builds!", please try running a later Spigot patch. I can't do anything about older Spigot releases blacklisting the plugin (preventing it from loading).

This is not something I can fix, as certain builds of Spigot prevent EchoPet from loading. Install a more recent Spigot build (patched from 1649).