“Unknown Error Occurred” in app purchases

Any time I try to make an in app purchase, I will make it through the double click feature get the check mark from that then it will close that pop up and say processing on the main app screen. After that an error message appears on the screen (“unknown error has occurred”) it’s been doing this for days. I’ve tried everything from resetting preferences to updating the software. I’ve checked all the payments on my Apple Wallet. I’ve restarted the phone, I’ve done everything that every panel has said. I have no idea how to fix it.