Still not enough data. No information about versions, no data on system environment, no description of what you're expecting to get and what you're actually getting. No logs. My crystal ball doesn't show me anything of that.
I've just checked the plugin with your settings on freshly installed Mibew Messenger. It works as intended.
If you see the plugin in the plugins list and it can be enabled (so it's state is 'Working'), then the plugin is installed correctly.
Double check your configuration. It's YAML, spaces matters.
Are you sure that you have operators group with id 1? Are you sure that there are at least one operator there? Are you sure that the operator from the group with id 1 is online? If answer to any of that questions is negative, auto invitation will not be sent.
Moreover, to send auto invitation the visitor should be tracked (i.e. shown in the appropriate list) and should not be invited before. Auto invitation is being sent only once.