The plugin will automatically detect Amazon Kindle devices during runtime.
To test your purchases, you do not need to create an Amazon developer account.
Install the Amazon App Tester (AAT) : Amazon App Tester
You need to create an amazon.sdktester.json file.
Example : amazon.sdktester.json Edit this to add your own Product Ids.
Put this file into the kindle sdcard with :
adb push amazon.sdktester.json /sdcard/
You can verify if the file is valid in the AAT and view the purchases.
Now, when you make a purchase the AAT will intercept, show the purchases screen and allow you to make a purchase. Your app will think a real purchase has been made and you can test the full purchase flow.
Add your apk into the "Live App Testing" tab. Add your IAP into the "In-App Items" tab. You must fill in your bank details first and submit your IAP so that the status is "live". Now your testers will be sent a link to the test version of your app. They can make purchases at no cost to test your app.
Amazon developer accounts are free. I found the Amazon store the easiest to submit to (compared with Googles play & Apple store). Required screenshots are the same size as a Nexus 7 so that is what I used.
I found the staff who checked my app very helpful (such as providing logcat output on request for example). Text is the same as other stores, except there is an additional up-to 10 bullet point summary of your app you can add.
When you submit your app to the store there will be a warning that google billing is detected in your code. When you submit your app for approval you can mention in the testing instructions for the Amazon reviewer that you are using a cross-platform tool and the google IAP code is not used. I dont know if this is necessary but my app was approved anyway.