A great example is to show a Justuno promo with a ShopMessage facebook checkbox or Opt-in CTA if this code is equal to true. Then, if the value is equal to false you could show an email opt-in promo instead.
After creating your facebook messenger optin promotion, copy and paste the code into your advanced ruleset. Once you've added the code within the ruleset you should be able to leverage shop message with Justuno.
Visit Justuno @ justuno.com