People are only prompted for this information if they have not provided it previously.
Go to Marketing Activities.
Select the app, and click Edit Draft.
In the social app editor, go to Sign-Up Flow > Person Capture.
Select the information you will request, and indicate the fields that are specifically required to sign up for your offer.
Include Marketing options:
Either way, participants will still receive the operational emails from your offer.
In the View & Edit window, click Show Edits and edit the messages in the share prompt.