Please note that you need to perform a clean installation of the plugin. Here's how to do it:
1) Save your old config.json.
2) Completely remove the plugin from the Plugins folder.
3) Delete the AntiPVEGrifering.pdb file from the Win64 folder (if the file is there).
4) Copy version 2.1 into the Plugins folder.
5) Replace the config.json with your old one.
6) Make changes to config.json as described above. You can always refer to config_commented.json to ensure everything is done correctly.
7) Installation is complete. Start the server.