Though email ID is registered with sandbox account, when we tried to purchase with sandbox account in both iPhone and iPad with iOS 16 beta 7 inapp- purchase is failing.
Sandbox In-App Purchase is failing from iOS beta 7 on iPhone and iPad.
Welcome to report this to engineering, any details you can add such as screen recording, sandbox Apple ID, time stamps or sysdiagnose. Feedbackassistant.Apple.Com
I am using these sandbox accounts to do purchase on iOS 16 Beta .