You might have multiple users mapped to a single billing contact in your billing system. If their payment fails, you might want to alert each user that their subscription is past due.
i.e. Joe@spotify.com is the billing contact, but Kate@spotify.com and Leela@spotify.com are also users.
Retain can target all the Spotify users with in-app messages. All you need to do is install the ProfitWell .js inside of your web app and pass in the customer ID inside the snippet to identify the logged in user. When a user logs in with the corresponding id of the customer that is past due, we'll deploy the in-app message.