See the Android integration instructions for information on how to integrate in-app messages into your Xamarin Android app. Furthermore, you can look at the sample application for implementation samples.
In-app messages will work by default if you’ve included the Appboy.bundle folder in your application. On Xamarin we don’t currently support in-app message custom styling. If you would like to customize your in-app message UI, implement the ABKInAppMessageControllerDelegate method
ABKInAppMessageViewController InAppMessageViewControllerWithInAppMessage(ABKInAppMessage inAppMessage); and return your custom view controller. That will make sure Braze passes you the in-app message object rather than displaying it for you. You will then have the option of displaying the in-app message object’s content manually.