Check out our Justuno integration.
It will appear after 3 seconds on this page.
With our Smart Display feature your store visitors can easily subscribe to your Messenger list if they are logged into Facebook.
If they are logged out of Facebook, they will only see the email subscription form.
You can read more about it here.
Our custom popup integrations need development work, we provide these integrations as a $99 add-on, on a monthly basis.