I see that Amazon is expected to begin Alexa ads on their Google Home competitor device in 2018. They are rumoured to be in talks with companies such as Colgate, Proctor and Gamble, etc about suggesting product or sponsoring product when a user does a voice search for a relevant product.
For example, if a user says: "Alexa help me buy toothpaste", it is likely that soon it will respond with something like "OK, I can look for a brand, like Colgate"--ie a target opportunity for a brand advertiser. The brand advertiser would pay Amazon for suggesting its product.
Currently we do not have a payment option built into Google Assistant but I would not be surprised if soon you will receive an option to provide both payment details and a delivery address.
https://www.cnbc.com/2018/01/02/amazon-alexa-is-opening-up-to-more-sponsored-product-ads.html
Is this something that you would find useful?