Thanks for posting! Could you please explain in more detail the "device registered using gmail account" part? Also, are you testing your IAP implementation against Amazon's server, or locally with the App Tester companion app and JSON file? Did you have a different version of the same app previously installed, and are now testing a different version over it? I would suggest uninstalling any other versions of this app (sideloaded or downloaded from LAT) and then re-try. If this is Live App Testing, then could you please confirm that your IAP implementation worked correctly on device (App Tester + JSON file) before you uploaded it? Finally, have you looked in the app's log files to see what is happening around that point you get this error -- this will give you the most insight on why there's this error and how to fix it. Thanks!