To manage your chat permissions go to Manage > Administration > Chat > Chat Permissions:

To set a new chat permission select a specific User, User Group or User Class in the Scope drop-down in the "From" section.

After that, use the Selection drop-down to select a specific User, User Group or User Class within the scope you selected:

Next, do the same in the "To" section:

Finally, toggle the Access button to enable or disable the chat permission. If the permission is enabled the Access button will turn green and if it’s disabled it will run gray.

When finished, click Add Rule  in order to save the new permission:

In the below example, the Basic User Class has been disabled from chatting with the Manager User Class.

If you would like to modify the permission for a specific "From" and "To" pair, simply toggle the Access button and the new permission will be automatically saved.

To delete a specific Chat permission, click the Delete button for that permission:

Note that user-specific permissions will override any group-level permissions. For example, when the Basic User Class is disabled from chatting with the Manager User Class, then no users in the  Basic User Class will be able to chat with users in the Manager User Class.

However, if you add a new permission that allows a specific user from the Basic User Class to chat with the Manager User Class, then such a user will be able to chat to the Manager User Class despite the group-level setting that would otherwise block the user.