So, girlfriend got Starbound today, of course she wants to play with me, but as a modded race. More specifically the Callistan and Elunite races. I tried booting up a server with said races, but I was prompted with a whoooole lot of errors. Server works fine without them. There a comprehensive guide I could read somewhere, or can someone tell me how to properly get these to work on multiplayer? Cheers!
Try 1 at a time and see which one is causing the errors, then post the error logs to the developers of that specific race.
I think (think being the key word here) you both have to have the mod for it to work, but you might be having a different issue I know nothing about. Hope you get it fixed either way though.
if both of you having the mods doesnt work, try looking into the files and finding the sprites for the races, then creating hats for their heads as a partial fix using hatter https://silverfeelin.github.io/Starbound-Hatter/