I'm also seeing this exact same behaviour in both Sandbox and Beta testing through Test Flight. THe first time a use purchases my in-app purchase they get the double prompt to buy. After that, the user only get's it once.
camow7
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution