The Shopping Actions API has been recently launched. But it is half-baked. When the control is on Alexa side and she asks the user if they wanted to add an item to cart and the user responds Yes or No, in the SessionResumedRequest handler, the skill wouldn't know the user response. It will only know that the request was "successful" but it doesn't mean that the item was added to cart. I have this issue in the skill certification and according to the support team that due to privacy and security reasons, third-party skills have no access whether the item was successfully added to cart or not. I'm guessing this is the same issue for the add to wishlist and purchase item shopping flows.

It would be awkward for Alexa to say a generic or non-concrete response after the user agreed or declined to add an item to cart. Something like, "Thank you for your request. If you added the item to cart, please complete the purchase at Amazon. If not, no further actions needed".

So please allow skills to know if the shopping action was truly successful or not.