So I've setup my VPS IP in the config file, but I get this error: Access denied for user 'root'@'*.*.*.*'. 

That IP is the IP of the game server, not the VPS, except the last '2' differs from the actual two digits.

Is this a plugin issue or something I'm doing wrong?

The error message clearly states you do not have access to the database, it has nothing to do with the plugin