I’m often asked by clients or see sellers posting this question: “What do I put in those platinum keyword boxes to optimize my listing?"
The short answer is nothing, leave that section empty. Thanks to the misleading name and proximity to the important Search Terms section these text boxes are often misinterpreted to be additional search keyword fields. This is not the case. They are utilized by sellers with Platinum level merchant accounts to build out their seller-specific storefront browse nodes. This allows them to customize their products in a categorization structure customers see when visiting their storefront.
The info box provided by Amazon provides a subtle hint:
Use this field only if you are a Platinum Merchant. This is used for defining the platinum keywords of your product. Child items should only use Platinum Keywords that are also assigned to the associated parent items.
The second part indicates that maintaining a parent-child relationship in your keyword choices is important for sellers using this feature.
Who are Platinum Merchants?
Gold and Platinum level sellers are part of an invite-only program extended to top-tier merchants. You’ll see very few Amazon help pages on these programs and while they aren’t exactly secret, information about them is on more of a “need to know” basis. The actual metrics Amazon uses to determine who to invite are intentionally kept secret, but its clear you must have: years of robust sales history, excellent customer support and feedback metrics, and AT LEAST six figures a month in revenue. In return for meeting these high standards you're given access to higher level benefits. At the Platinum level these include improved odds of winning the buy box (but not enhanced appearance in search results as has been rumored), weekly payouts and unfettered access to all product categories.
Why is this in my listing if I can’t use it?
Amazon provides many fields for all sorts of data that is in no way relevant to every product or seller. Take a look in the “More Details” tab in your listing backend. It's likely only a few of those are applicable to your listing as well.
Don't waste any time worrying about the Platinum Keywords section. It has no relationship to your far more important Search Terms fields despite the proximity and name, and has no effect on your search ranking or relevance considerations for Sponsored Product Ads.