Amazon Affiliate ID

You add your Affiliate ID in the plugin’s Options page (along with your Access Key ID and Secret ID).

You should not need to add it any other place.

The buy link may not look exactly like a normal Amazon link because it has additional items in it, so you may not be able to tell by looking at it.

Amazon has a link checker in your account that you can use if you ever want to make sure a link will give you proper credit.
Login to your Amazon account and go to the link:
https://affiliate-program.amazon.com/gp/associates/network/tools/link-checker/main.html

or in the Links and Banners menu, it will be the bottom item (Link Checker).

You simply copy the link in question and paste it and check it. It will tell you if you will get proper credit for a sale made with the link.

Regards,
Don