Also, this page talks about targeting the specific APP :
https://experienceleague.adobe.com/docs/campaign-standard/using/communication-channels/in-app-messaging/preparing-and-sending-an-in-app-message.html?lang=en#sending-your-in-app-message
is the app showing up as registered in the ACS instance? Are they using
an OOTB message type: Target users based on their Campaign CRM profile
(inAppProfile)Target all users of a Mobile app (inAppBroadcast)Target
users based on their Mobile profile (inApp) I...