How can I send a WhatsApp message to users who have not opened my mobile app recently?

Directly creating a segment that combines 'WhatsApp users' and 'Last application open > 7 days' will likely result in zero users. This is because the Last Application Open attribute is only tracked for mobile app devices (iOS/Android), not for WhatsApp channel records.

To achieve this targeting, you can use a Customer Journey, provided your users' mobile app devices and WhatsApp numbers are linked by the same User ID.

Here is how to set up the Customer Journey:

1. Start the Journey: Begin your journey with an entry element, such as Audience-based Entry. In its settings, make sure to enable the “Include all user’s devices” option. This ensures the journey pulls in both the mobile and WhatsApp devices for each user.
2. Add a Condition Split: Drag a Condition Split element into your journey. Configure it to check for users in a segment where “Last application open is more than X days ago.” Again, it is crucial to enable the “Include all user’s devices” option within this element's settings.
3. Send the WhatsApp Message: In the 'Yes' branch of the Condition Split, add the Send WhatsApp Message element.

This setup works because the Condition Split evaluates the 'last open' date across all of a user's linked devices. If their mobile app device meets the inactivity criteria, their entire profile—including their WhatsApp device—proceeds down the 'Yes' path. The final step then correctly sends the message only to their WhatsApp number.