So this is the first time that I am posting on any site about Minecraft and I hope that it helps someone in the future. So if you go to the site for FTB Unstable 1.12 from the twitch client it will bring you here. but that website does not give you much help when it comes to building a server for the mod pack. It will give you the latest downloads and tell you that you are on your own and will have to trouble shoot on your own. So I wanted to see if google had anything else on the mod pack and I found this. http://legacy.feed-the-beast.com/modpacks/FTBUnstable112 and on this page it says there are currently no server versions for this mod pack. In order for it to work as a server you have to update the Extra Utilites 2 file from extrautils2-1.12-1.5.2.jar to extrautils2-1.12-1.6.1.jar and it will work. I hope this helps and if anyone has any questions I would be glad to help as much as I can.