The Buy on Amazon screen in the app decides two things: where each Buy on Amazon button sends the shopper, and whether Amazon can credit you for the click. The look of the button is set in your theme instead. See Buy on Amazon button.
Most stores never need to touch this screen. If your products are mapped and price sync is running, the app already knows each product's Amazon link for each market. Come here when you want to point a button somewhere specific, or when you want attribution tracking.
These apply to every Buy on Amazon button on your storefront. Click Save store settings to apply them.
Optional. If you set a URL here, every button on every product in every market links to it, and nothing else is consulted. It sits at the top of the link priority order.
This is a blunt instrument, and that is exactly why it is useful. Use it when you want all traffic sent to your Amazon storefront or brand page rather than to individual listings, or when you have a small catalogue where mapping is not worth the effort and you would rather have one link that always works.
Leave it blank to use per-product and synced links, which is what most stores want.
On by default. Your store's tab stays open and Amazon opens alongside it. Turning it off sends the shopper away from your store in the same tab. There is rarely a reason to do that.
Turning this on reveals two more fields: Associate / attribution tag (tag=) and Extra URL parameters.
Amazon Attribution is Amazon's measurement programme for traffic that comes from outside Amazon. When you send a shopper to Amazon with a tag on the URL, Amazon can tie the click, and any resulting purchase, back to you. That gets you two things:
Put your tag in Associate / attribution tag (tag=). It is added to the outbound link as the standard tag= parameter. Amazon issues the tag; the app does not create one for you.
Extra URL parameters takes any further tracking parameters you want appended, for example campaign identifiers you already use in your own reporting.
Note
Attribution parameters are appended to whichever link the app decides to use, including a store-wide override URL and a manually entered per-product URL. You do not need to paste tags into each URL by hand. Set the tag once here and every button carries it.
Below the store-wide settings you can search for a product and choose how its links are worked out. Each product has a Link source with three options.
The app uses the Amazon link it already synced for the variant, matched to the shopper's market. This is the right choice for almost every product, because it needs no maintenance: map the variant to an ASIN, let price sync run, and the correct marketplace link appears by itself. See Product Mapping.
You enter a single URL and every shopper gets it, whatever market they are in. Use this when you have one canonical listing you want to push everyone towards, or when the product is only really sold in one marketplace and you would rather send an overseas shopper there than to a local Amazon that does not carry it.
You enter a URL for each Amazon marketplace individually. This is the precise option. Use it when you are running separate attribution links per marketplace, or when the listings differ enough between marketplaces that you want to control each one.
You do not have to fill in every marketplace. A blank per-marketplace field falls back to the synced link for that market. So you can hand write the link for the two marketplaces you care about and let the app handle the rest. If no synced link exists for that market either, the button does not render there.
When a button renders, the app picks a link in this order and stops at the first one it finds.
Attribution parameters are appended to whichever link wins.
If none of the four produces a URL, the button is hidden on the storefront entirely. That is by design, and it is the most common reason a merchant reports a missing button. See Buy on Amazon button for the checklist.
Warning
An override URL beats everything. If you set one and then wonder why your carefully entered per-marketplace links are being ignored, clear the override.
For most stores the setup that needs the least ongoing work is this. Leave the store-wide override blank. Keep Open Amazon in a new tab on. Turn on attribution and enter your tag once. Leave every product on Use synced Amazon links (default), and make sure the variants that matter are mapped. Then reach for the per-product options only where the default link is not the one you want.
See also the Amazon Price block, which uses the same synced links, and Market mappings, which decides which Amazon marketplace each Shopify market resolves to.