I'm having difficulty using In-App Messaging and I do not know how to solve this problem.
I created a campaign and sent a test to a device, and this test never succeeds. Today I was surprised by the message being displayed from a test I had done three days ago.
I've read and reread all of the In-App Messaging documentation and all the steps were followed correctly, but I've never been able to make it work.
After all, does In-App Messaging work on iOS or is it just a proposal to maybe work in the future (if it works)? Honestly it's pretty frustrating something so simple does not work.
You may be running into a bug that was recently introduced. The fix will be available in the upcoming Firebase 6.1.0 release.
In the meantime, you could get the functionality back by installing to Firebase 5.17.0 or earlier, along with FirebaseInAppMessaging 0.12.2 or earlier.