Updating a Modpack
You may see an error when a client connects with a version of the pack that is different from the one running on your server. The best way to ensure that you don’t run into this issue is to make sure everyone is running the latest version.
Modpacks are frequently updated to fix bugs or add new features. As a result your server will need to be updated either manually or using the Modpack Manager.
This is destructive process! If you make a mistake you may loose progress that you won’t be able to recover! Make sure to take a full backup before continuing!
Using the Modpack Manager
After making a full backup of your server including every file and folder in the root directory, make sure your server is stopped and delete the mods folder in the root directory. Then navigate to the Modpack Manager and find the Modpack you have installed, click install, and select the version you want to install. *Do NOT select Format Server*.
After the installation process completes, start your server and connect with an updated version of the client modpack. If it worked you should be able to connect. If you can’t connect, then you’ll want to revert to the backup you took and try again.
If you’re still having issues on your 2nd attempt, try updating the pack manually using the steps below.
Manually Updating
If the pack your using isn’t available in the Modpack Manager or the Modpack Manager isn’t working, then you’ll need to start with getting a zip file of the Server Files for the Modpack. CurseForge, Modrinth, FTB, and ATlauncher refer to this zip file as a “Server Pack” and it should contain all of the mod and configuration files for running the server from scratch.
After making a full backup of your server including every file and folder in the root directory and then uploading the Server Pack mentioned above 
Using SFTP, you’ll need to delete the mods folder from the root directory. Then you’ll decompress the Server Pack archive from the File Manager. This will do the same thing that the Modpack Manager does, overwriting existing files and adding new ones where they didn’t exist before.
After the installation process completes start your server and connect with an updated client. If it worked you should be able to connect, if you can’t then you’ll want to revert to the backup you took and try again.
If you’re still having issues after your 2nd attempt, reach out to us on Discord or through a support ticket and we’ll do our best to help!