An in-app-message is usually a popup that is shown to your app customer. They are used to educate users or promote some offer, service or event. For example, you can use them to announce a new feature or advertise a special offer.
Marketeers can run in-app campaigns to help with retention and engagement. There are tools to support in-app notifications and messages which allow marketing to compose dynamic popups and schedule them to be shown to customers. Check out CleverTap, Localytics, AppCues and Braze.
We think this is a great tool for marketers to have at their disposal. We've seen it used well for new product announcements in smarthome apps. And it would be useful for fast-response situations, such as when services have been interrupted or changed by unexpected events like the Coronavirus outbreak.