As far as I know, you can only see notifications at the endpoints, with no way to intercept them. However, I would strongly encourage you to use a real device for all your testing. It doesn’t have to be an Amazon device, in fact you can use your non-Amazon tablet or smartphone for testing IAP. For that, you need to install the Amazon Appstore client app on it, see:
https://www.amazon.co.uk/gp/mas/get/android/
and also the App Tester companion app:
Login to the Amazon Appstore app on your device with the same account you use to login to your Developer Portal, and you should be able to see your apps in the beta environment (Live App Testing) as well. Such a setup will let you test IAP in a more realistic setting. Hope that helps.