As long as the request is valid, Product Advertising API will try to process it. There are times when Product Advertising API returns a result and an error. For example, if you had a batch or multi-operation request, one item might be found, the other not. In that case, IsValid would be true, the response would contain the item attributes of the item found, and the response would also contain an error message that the second item could not be found. Product Advertising API attempts to return as much information as possible even when an error prevents the successful completion of a portion of a request.