On the page Interactivity, tab Eureka settings, you can find a checkbox Networking features. This checkbox should be on if you are using the networking features in your app. It enables the Settings tab on the profile page in the app, where users can set whether they want to be in the attendee list and whether they want to allow other users to send them messages.
Please note that if you change settings, you have to publish a release before these changes are applied!
When the checkbox is off, the Talk settings on the user profile in the app are not visible. This can be useful if you're not using any of the networking features (attendee list, session chat or event feed), as your users will then not be bothered with non-relevant settings.