Select a message from the dashboard and create a new campaign.
Select audience as filter from “Target Users” on the bottom of the screen, when creating a new campaign.
Make sure that the In-App messages are being correctly displayed on the target user device that was added.
If it is not being properly displayed, there may be a problem with the execution timing of the event. Please refer here if this is the case, and either change the execution timing of the event, or change the displayed trigger event.