Two issues:
In-app promo code for a consumable item is not delivering/unlocking that item for the customer. The promo code says it's redeemed and can't be re-used, which shows the customer is following the correct process.
In-app promo code for a subscription will not unlock. It claims the code can only be used from a gift card ('This requires a gift card with a box around the code'), and tells the customer to use a camera with the nonexistent gift card. Obviously we have given a code to the user, not a gift card.
Both in-apps work correctly if purchased from within the app as a test purcase, so it's not a code/setup problem.
It's not user error.
The app has been live for at least 6 years.
What's changed?