Serversync Version: 4.2.0

Minecraft Version: 1.16.5

Issue:

This is my config
When I set this up and open ServerSync, it just flashes and disappears without any logging.
When I only kept the sync mod function, everything worked fine.
But my server requires players to sync missions.

Presumably you figured this one out.

You probably need to set up config as a managed directory, I would usually use push mode personally as you probably don't want to wipe out user configuration files.

"directories": {
  { "path": "config", "mode": "push" }
}